XSL-FO/CSS
Comparison

CSSer’s view of XSL-FO

• Source XML or HTML must be transformed into the XSL-FO vocabulary

  Transformation has advantages and disadvantages. CSS was designed to support stream-based or incremental formatting [1995], which is part of why CSS selectors cannot match ‘down’ into the content of the current element or ‘forward’ to the structure of following elements. A transformation stage, on the other hand, typically (although less so after XSLT 3.0 added streaming for XSLT) requires the whole document to be available, but it does allow style decisions to be made based on the whole document. Transformation also allows the content to be duplicated and reordered to, for example: generate tables of contents and indexes; sort the rows of a table; or calculate subtotals.

  Formatting paged media using CSS 3 typically requires some form of transformation anyway. This includes generating the running elements that are taken out of the flow and used in headers and footers, as well as generating tables of contents and indexes.

• Separate attributes for each property is verbose

  XSL-FO is designed to be the result of an XSLT transformation. XSL-FO was not meant to be read, let alone authored, by humans. It does happen, of course. When XSL-FO is serialized as XML, it is straightforwardly usable in XML editors, etc., and it is as human-legible and as reasonably clear as any other XML or HTML document.

  When XSL-FO is generated using XSLT, the XSLT is less verbose than the XSL-FO that it creates. An FO and its properties can be generated from literal elements and attributes inside an XSLT template, but a single XSLT template can be used many times to generate multiple copies of the FO. Attribute sets in the XSLT are defined once and are used in multiple places in the XSLT. An XSLT template can contain more than just literal elements and attributes to copy to the result: the XSLT can include as much logic as is necessary to be able to conditionally generate the correct FOs, their correct properties, and the correct property values for any given context.

• JavaScript could be used instead of XSLT

  Yes, JavaScript can be used to generate tables of contents, indexes, and so on by manipulating the DOM of the document, but whatever JavaScript solutions exist have been bespoke code. Over the last 20 years, there hasn’t been a standard, widely used, general purpose JavaScript library that matches both the path-matching ability of XPath and the declarative templating mechanism of XSLT. AH Formatter will format a correct XSL-FO file no matter how it was created.

• XSL-FO properties inherit but do not cascade

  The role of the cascade is taken by the XSLT transformation.

  In XSLT:

  • One XSLT stylesheet can import another, similarly to how @import imports another CSS style sheet
  • The ‘match’ patterns in XSLT templates have a default priority based on the specificity of their XPath pattern, similarly to more specific CSS selectors overriding more general ones. In addition, an XSLT template may be given an explicit numeric priority.
  • When there is more than one matching template with the same precedence, the one that occurs last is used, similarly to two CSS rules that have the same weight
  • An XSLT ‘attribute set’ is a named set of attribute definitions. The attribute definitions are reevaluated in each context where the attribute set is used. Multiple <xsl:attribute-set> with the same name are aggregated, with definitions for individual attributes in an <xsl:attribute-set> with higher precedence overriding definitions in other <xsl:attribute-set> that have lower precedence. An <xsl:attribute-set> can also reuse attribute definitions in other, named attribute sets. Attribute sets are not quite the same as on-the-fly building up of the properties to apply in a particular context based on the cascade of @import rules and specificity of CSS selectors, but they do make it easy to apply a group of properties in particular contexts.

• FOs are like elements with fixed display property values

  In CSS, all that you have is the source document (unless, as noted previously, you have augmented the original source document to create tables of contents, etc.), and the display property, like all properties, is applied as the document is formatted. With transformation before formatting, the decisions about how to format each part of the source document are part of the transformation, so there is no need for on-the-fly changes using a display property.

• XSL-FO does not have variables

  CSS gained variables only recently, but variables are not needed in XSL-FO. XSLT has variables (which have scope and which can be passed between templates), so any calculations based on variables or any substitution of constant values can be handled in XSLT.

• XSL-FO can’t be used for both web and print

  XSL 1.1 defines how to handle a page that extends indefinitely in one or both dimensions and it also includes some interactive FOs, but neither of those has been widely implemented because few users have ever expressed interest in them.

• CSS is easier to learn that XSL-FO

  The basics of CSS syntax are easy to learn, but there is an expanding list of CSS selectors and pseudo-elements to be remembered, plus many CSS properties have their own micro-syntax for expressing their value. XSLT and XSL-FO are XML vocabularies, so most of their syntax is easily understood by anyone who can read XML or HTML. However, XSLT and XSL-FO attempt more than CSS, so it is not surprising that there is more to learn. XSLT is a Turing-complete declarative language for specifying transformations, whereas CSS is a declarative language for specifying styles. People who are used to imperative programming languages where they specify every step of the program can have trouble adapting to the XSLT model where the structure of the source document can determine the program flow.

  XSL-FO provides more control than CSS over, for example, the selection of page masters and the content of headers and footers, so it has more FOs and properties for those areas.

• There are more CSS users than XSL-FO users

  True. However, comparatively few CSS users are familiar with using CSS to generate paged media. If you want to learn more about CSS for paged media, see Introduction to CSS for Paged Media [ITCFPM], available from the Antenna House website.

XSL-FOer’s view of CSS

• CSS ‘just decorates the tree’

  Decorating the tree of elements fits with the original goal of CSS to support streaming or incremental formatting. [1995] XSLT, in contrast, can use any part of the document, or of a different document, when deciding which template to use in the current context. By using modes, XSLT can process the document or parts of the document multiple times in different ways.

  The structure of the XSL-FO document does not need to match the structure of the source document: the XSLT stage can generate literal elements as well as copy all or part of any node in the source document. An XSLT template can select which nodes to process next rather that just processing the children of the current node.

• CSS selectors won’t look ‘down’ or ‘forward’

  CSS selectors can match on the current element, its class (or classes), its attribute values, its ancestor elements, and its preceding elements. Selectors won’t, however, match on the string value of an element or on any aspect of the type and arrangement of an element’s descendent elements. In contrast, the entire document (and possibly other, external documents) is available to the XSLT processor, and style decisions can be made based on more than just the context of the current element.

• CSS only operates on elements

  CSS selectors only apply to elements. In contrast, XSLT templates can match on text nodes, text nodes with particular values, or text nodes in particular contexts (possibly with particular values) and can generate FOs based on those text nodes. XSLT can similarly match on comments and processing instructions and generate FOs.

Page master

A ‘page master’ is the specification of the size and overall layout of a page. A formatted document where all the pages are essentially the same could have just one page master. A formatted document could require multiple page masters if it has, for example: title page; different margins on right and left pages; one-column body text and a multi-column index; landscape pages for wide tables; or wider margins on table of contents pages.

Page masters in XSL-FO are defined using <fo:simple-page-master>. An <fo:simple-page-master> can define up to five types of regions. <fo:region-body> receives the main content of the document, and the other regions receive the content that makes up the headers and footers on each page. Omitted regions do not generate any areas when the <fo:simple-page-master> is used to generate pages. XSL 1.1 added the ability to define multiple <fo:region-body> on one page and to direct one or more flows to one or more regions on the page using <fo:flow-map>.

Page masters in CSS are defined using an @page rule. [CSS3-Page]

Page region layering

XSL 1.1 specifies that the regions follow a fixed sequence in the XSL-FO. AH Formatter relaxes this and allows the regions to appear in any sequence. AH Formatter renders the areas for the regions in the sequence in which the regions appear in the XSL-FO: z-index does not apply to the regions, so the declaration sequence is a way to control which regions can overlap other regions. If <fo:region-body> is last, it can overlap content from the other regions.

z-index applies to CSS page-margin boxes. It can be used to control the layering of page-margin boxes that have content that overlaps.

Spreads

A ‘spread’ is two facing pages.

AH Formatter has an <axf:spread-page-master> extension for XSL-FO. The background of an <axf:spread-page-master> extends across both pages, and regions defined in the <axf:spread-page-master> can span across more than one page.

CSS does not have any support for specifying spreads. The AH Formatter extension is not available with CSS because CSS does not provide the same control over the sequence of page masters as in XSL-FO.

Page size

Page size in XSL is specified with the page-height and page-width properties, or with the size shorthand for setting both at once. The XSL 1.1 size is based on the CSS 2 size property, but that size was removed in CSS 2.1 and not reinstated in CSS 2.2. AH Formatter implements a superset of the CSS Paged Media Module Level 3 size property, which adds keywords for several standard page sizes.

Page size in CSS is specified using the size property. The extended set of page size keywords is similarly available in CSS.

Selecting page masters

The content in an XSL-FO document is contained in one or more <fo:page-sequence> FO. Each <fo:page-sequence> specifies which <fo:simple-page-master> to use or, indirectly, which set of <fo:simple-page-master> to use. The <fo:page-sequence> can refer to a <fo:page-sequence-master> that sets out which <fo:simple-page-master> to use and in what sequence.

The sequence of page masters can be any sequence of:

• One page master, possibly with a limit to the number of times it can be repeated

• A choice between alternative page masters, possibly with a limit to the number of times that the choice can be repeated. The references to the alternative page masters each have three sub-conditions for deciding whether to use that alternative. When a new page is to be generated, the alternatives are considered in sequence, and the first alternative for which all three subconditions is true is chosen.

  The sub-conditions are:

  • The page is either first, last, only (both first and last), neither first nor last, or any page in its page sequence
  • The page number is either odd, even, or any (i.e., whether it is odd or even will not affect the choice)
  • The page is blank, is not blank, or is any (i.e., whether or not it is blank will not affect the choice)

  The sub-conditions are expressed as properties. The any value is the default for each property, so when choosing an alternative, you only need to specify the sub-conditions that affect the choice.

For example, a document with different margins on odd and even pages could have two <fo:simple-page-master> named OddPage and EvenPage. The <fo:page-sequence-master> for choosing the correct page master could be:

<fo:page-sequence-master master-name="PageMaster">
  <fo:repeatable-page-master-alternatives>
    <fo:conditional-page-master-reference master-reference="OddPage"
                                          odd-or-even="odd"/>
    <fo:conditional-page-master-reference master-reference="EvenPage"
                                          odd-or-even="even"/>
  </fo:repeatable-page-master-alternatives>
</fo:page-sequence-master>

(Note that odd-or-even="even" is not strictly necessary here because any page that did not match the previous odd-or-even="odd" is, by definition, an even page.)

CSS does not have a separate mechanism for predetermining the sequence of page masters. (Even in XSL-FO, it is only partially predetermined, because which page is the last page, or which pages are blank, is not known until the document is formatted.)

In CSS, any element that can cause a page break before or after itself can cause a change in @page rule by specifying the page property with a value that is different from the value of its parent or preceding sibling element. As an extension to the current CSS definition, AH Formatter allows a sequence of multiple names in the page property, and AH Formatter uses each specified @page rule in turn when generating pages. If the element generates more pages than there are names in the page property value, AH Formatter continues to use the last name for the remainder of the pages.

Nested page sequences

XSL 1.1 does not allow page sequences to be nested: all of the page masters to use and conditions for their sequence of use are determined by the <fo:page-sequence-master> referred to by an <fo:page-sequence>.

AH Formatter allows <fo:flow> to contain children <fo:page-sequence> FOs. Formatting a nested <fo:page-sequence> is equivalent to ending the containing <fo:page-sequence>, formatting the <fo:page-sequence> as if it were another top-level <fo:page-sequence>, and then formatting the FOs after the <fo:page-sequence> as if in a copy of the original containing <fo:page-sequence>.

CSS does not differentiate between top-level elements and lower-level elements that can change the @page that is being used. As stated previously, any element that can cause a page break before or after itself can cause a change in the @page rule that is being used.

Multiple body regions on one page

XSL 1.1 added the ability to define multiple <fo:region-body> in an <fo:simple-page-master> and also multiple <fo:flow> within an <fo:page-sequence>. One or more <fo:flow> can be directed to one or more <fo:region-body> on a page. Which <fo:flow> are directed to which <fo:region-body>, as well as the sequence in which multiple <fo:flow> are directed to one (or more) <fo:region-body>, is controlled by an <fo:flow-map>, which was also added in XSL 1.1.

CSS does not have a comparable feature at present.

XSL-FO

The areas generated from the four ‘outer’ regions—<fo:region-before>, <fo:region-after>, <fo:region-start>, and <fo:region-end>—receive content from <fo:static-content>. Each region has a default name based on its type, but different region-name values can be specified. An <fo:static-content> directs its content to a region with the same region-name value as the flow-name property value of the <fo:static-content>. This makes it possible to set up the static content for multiple sorts of pages and use only the applicable static content on each page. It also makes it possible to, for example, direct the contents of one <fo:static-content> to the outer, left-hand region on left-hand pages and to the outer, right-hand region on right-hand pages.

Variable content that should appear in the header or footer, such as the current chapter title, is declared in an <fo:marker>. Any number of <fo:marker> can be included as the first children of <fo:flow> and of many of it descendent FOs. An <fo:marker> can contain any combination of text, inline-level FOs, and block-level FOs, but it does not generate any areas. Instead, its children are available to be retrieved and formatted by an <fo:retrieve-marker> that is within an <fo:static-content>.

As stated previously, the applicable <fo:static-content> provides the complete content for one of the outer regions on the page, and it is only those applicable <fo:static-content> that actually retrieve and format the children of an <fo:marker>. An <fo:static-content> contains one or more block-level FOs. One or more <fo:retrieve-marker> can be present as the only content of the <fo:static-content> or as siblings of block-level FOs. The block-level FO or FOs can contain any number of <fo:retrieve-marker> in any part of their content.

The correspondence between the marker-class-name property on the <fo:marker> and the retrieve-class-name property on the <fo:retrieve-marker> connects an <fo:marker> and an <fo:retrieve-marker>. Any name token can be used; for example, chapter-title and xyzzy are equally allowed. Sibling <fo:marker> cannot use the same marker-class-name value.

If the <fo:marker> for the chapter title is:

<fo:marker
  marker-class-name="chapter-title">A<fo:inline
    font-variant="swash(1)">&</fo:inline>B</fo:marker>

then the <fo:static-content> of the header can be:

<fo:static-content flow-name="xsl-region-before">
  <fo:block font-size="10pt" text-align="center">
    <fo:retrieve-marker retrieve-class-name="chapter-title" />
  </fo:block>
</fo:static-content>

The content of the <fo:marker> is formatted in place of the empty <fo:retrieve-marker>. The content is formatted as if it had the same ancestors as the <fo:retrieve-marker>; that is, the content inherits property values from the context of the <fo:retrieve-marker> within its <fo:static-content> and not from the context of the <fo:marker> in its parent FO.

There can be multiple <fo:marker> with the same marker-class-name in the FO document (just not with the same parent FO). Multiple FOs that have <fo:marker> children with the same marker-class-name could generate areas on the same page. To continue with the example, unless each chapter starts on a new page, there could be both the end of one chapter and the start of the next chapter on the one page, and some books have complete chapters that are less than one page, so there could be part or all of three (or more) chapters on one page.

An XSL formatter considers <fo:marker> related to areas on the current page and, possibly, on preceding pages. It chooses a preferred <fo:marker> based on the retrieve-position and retrieve-boundary property values of an <fo:retrieve-marker>:

• retrieve-position specifies a preference based on the areas generated by the parent FO of an <fo:marker> compared to the areas generated by other identically named <fo:marker>. retrieve-position can have values first-starting-within-page, first-including-carryover, last-starting-within-page, and last-ending-within-page.
• retrieve-boundary specifies how far back to find a carried-over <fo:marker>. It can have values page, page-sequence, and document. retrieve-boundary can be useful to stop a marker ‘leaking’ into pages where it is not wanted: for example, an epilogue that does not need a running title in the header could use the same page masters as chapters if:
  • The epilogue is in a separate <fo:page-sequence>
  • The epilogue does not contain an <fo:marker> for the running title in the header
  • The <fo:retrieve-marker> for the running title in the header omits retrieve-boundary to use its initial value of page-sequence.

Page numbers in the header are generated using <fo:page-number>. The total number of pages shown in page numbers such as “Page 1 of 5” can be generated by using <fo:page-number-citation-last> with a ref-id value that refers to the ID of the <fo:page-sequence> or other FO that encompasses all of the FOs that generate those pages.

CSS

In CSS, every page has 16 page-margin boxes that are always available to receive content. The names of the page-margin boxes are fixed.

A page-margin box is generated only if it has content; that is, if the value of its content property is not none. none is the computed default, so page-margin boxes ordinarily do not generate any boxes. This differs from XSL-FO, where the areas from <fo:region-before>, etc. can generate an area that has, for example, borders and a background color even when it has no content generated from an <fo:static-content> (provided that the extent property of the region is not 0pt).

Content can be either:

• Inline-level content that is any combination of literal strings, values of named strings, counter values, leaders, cross-reference text, or images
• A running element that has been removed from the flow using position: running(…); and is retrieved using content: element(…);.

The string-set property sets one or more named strings. For example, to set the chapter named string to the text value of the current element:

H1 { string-set: chapter content(); }

The string name is followed by a list of string values that are concatenated to form the value of the named string. Setting a named string overwrites any previous value set earlier in the document. An element with display: none; can still set named strings.

string(chapter) in the content property of a page-margin box retrieves the value of the string named chapter. Multiple elements on one page can set the same named string, so string() has an optional second argument to select one of the possible strings. The defined values are first (default), start, last, and first-except.

Using position: running(name); is similar to using string-set, except that position: running; takes the current element out of the flow—similar to specifying display: none; . content: element(name); inserts the named running element into the page-margin box. element() also has an optional second argument to select one of the possible running elements with the same name: first (default), start, last, and first-except.

A running element inherits from its original position in the document. This is the opposite of <fo:marker>, where the marker contents inherit from the position of the <fo:retrieve-marker> in its <fo:static-content>.

counter(page) in the content value of a page-margin box generates the current page number.

Leaders

XSL-FO and CSS both support leaders: XSL-FO using <fo:leader>, and CSS using leader() in the value of the content property. Leaders in XSL-FO can be unaligned or aligned to the reference area or page. AH Formatter does not support alignment to the page, but leaders can be aligned to the start, center, or end of their area. Leaders in CSS are always aligned to the end edge of their containing block. Leaders in XSL-FO have a specified length (which can have minimum, optimum, and maximum components), whereas leaders in CSS always expand to fill the available space on the line. AH Formatter provides the axf:leader-expansion extension property for XSL-FO leaders to expand to fill the line and the -ah-leader-length extension property for CSS leaders to have a specified length.

Overflow

An <fo:block-container>, <fo:inline-container> or a CSS block can have a fixed height and/or width. It is possible for the content of the FO or CSS block to overflow the specified dimensions. On paged media, the content can overflow the available height or width, regardless of whether the area has a fixed size. XSL-FO and CSS both define the overflow property that specifies whether and how the content is clipped when it overflows the area. XSL-FO extends the CSS overflow by adding two more keywords.

AH Formatter extends the XSL-FO overflow with more ways to recover from an overflow. The extended overflow property is available with both XSL-FO and CSS. AH Formatter can either replace the text of the area or condense the existing text by modifying values of one or more properties until the text fits in the area. Properties that can be adjusted are font-size, font-stretch, line-height, and letter-spacing.

Hyphenation

XSL-FO and CSS both support hyphenation: XSL-FO using hyphenate and related properties, and CSS using hyphens and related properties. AH Formatter provides some of the XSL-FO properties that do not have CSS equivalents as extension properties in CSS. AH Formatter provides additional extension properties for hyphenation in both XSL-FO and CSS.

Neither XSL-FO nor CSS define how a formatter determines where to hyphenate words. AH Formatter implements a hyphenation algorithm for multiple languages, and it can also use T_EX hyphenation dictionaries. Hyphenation exceptions can also be specified in an external hyphenation information file and, for XSL-FO, <axf:hyphenation-info> elements can be included in <fo:declarations> in the XSL-FO document. The AH Formatter Option Setting File can also include a list of unbreakable words that, obviously, will not be hyphenated.

XSL-FO

An <fo:footnote> contains both an <fo:inline> for the marker that is generated at the point where the <fo:footnote> occurs and an <fo:footnote-body> that contains the actual footnote. The <fo:footnote-body> includes whatever marker should appear with the footnote: there is no specific FO for this, although the footnote body is often formatted as an <fo:list-block> so that a marker can be positioned correctly.

The content of the <fo:footnote-body> is ordinarily formatted in the footnote-reference-area of the bottom of the <fo:region-body>. The footnote-reference-area is implicitly present in every <fo:region-body> but it is generated only if the page contains one or more footnote areas. The footnote-reference-area cannot be defined as part of defining an <fo:region-body> in the <fo:simple-page-master>. If an footnote-reference-area is generated, it contains any areas generated by an <fo:static-content flow-name="xsl-footnote-separator"> in the current page sequence followed by the areas generated from the <fo:footnote-body> from footnotes on the current page (as well as areas from any footnotes carried over from previous pages). The fo:static-content is used to, for example, generate a horizontal rule (often using an <fo:leader> with a fixed width) or force some white-space between the body text and the footnotes.

While XSL 1.1 defines footnotes as appearing only in the footnote-reference-area that spans the bottom of an <fo:region-body>, AH Formatter can generate footnotes that are page-wide or column-wide or are sidenotes at the ends of lines of body text. Page-wide footnotes can be placed on the current page or only on odd-numbered pages or only on even-numbered pages. Column-wide footnotes can be placed in the current column or the first, last, inside, or outside column on the page. Sidenotes can be placed in the <fo:region-start> or <fo:region-end> at the start, end, inside, or outside of the line containing the sidenote marker.

AH Formatter can also suppress duplicates of footnotes that would appear more than once in the same page or column.

XSL 1.1 does not define a way for footnote numbers to restart on each page. The text of the footnote marker in the <fo:inline> and any corresponding mark in the <fo:footnote-body> are expected to be generated by the XSLT that generated the XSL-FO. AH Formatter can format a provided numeric marker using any supported number format or counter style. Alternatively, AH Formatter can generate the footnote number to use and format that. If desired, the generated footnote numbers can be reset at page, odd-page, even-page, or column breaks. To reset footnote numbers, for example, for each chapter, axf:footnote-number-initial="1" can be specified on each <fo:page-sequence>.

CSS

Specifying float: footnote; for an element removes the element from the flow and causes it to be formatted as a footnote. Similarly, specifying float: sidenote; causes an element to be formatted as a sidenote. A ::footnote-call (or ::sidenote-call) pseudo-element is generated in place of the element. A ::footnote-marker pseudo-element is placed at the beginning of the footnote element, and the combination is formatted in the footnote area. A ::sidenote-marker is similarly created for a sidenote.

CSS, like XSL 1.1, defines that footnotes appear only at the bottom of a page. Sidenotes (when they were still in the GCPM Working Draft) were shown as floating to the margins of the page. The footnote area is defined by an @footnote rule in the applicable @page rule (and the sidenote area by an @sidenote rule). In CSS, the @footnote rule is expected (or required) to contain float: bottom;, which corresponds to or indicates the position of the footnotes. AH Formatter allows the float property to be any supported value.

The default stylesheet styles the ::footnote-call pseudo-element as a superscript digit and the ::footnote-marker as an inline list-item marker. The default content of both pseudo-elements is the value of the footnote counter. The current GCPM Working Draft states that the footnote counter may be reset for each new page. The AH Formatter default stylesheet does not reset the counter, so footnote numbers default to incrementing all through the document. Footnote numbers can be formatted using any supported counter style.

-ah-suppress-duplicate-footnote suppresses duplicate footnotes in the same page or column in CSS formatting.

Table header and footer

Tables can have header and/or footer rows in both XSL-FO and CSS. The header and footer rows are repeated when the table breaks across a page or column. XSL 1.1 defines table-omit-header-at-break and table-omit-footer-at-break properties that specify whether the table header or footer, respectively, should be omitted when the table breaks. AH Formatter adds the column keyword for specifying that the header or footer should be omitted at column breaks but not page breaks. CSS does not define corresponding properties, but AH Formatter provides the -ah-table-omit-header-at-break and -ah-table-omit-footer-at-break extension properties for use with CSS.

An <fo:table> can contain <fo:retrieve-table-marker> as a descendent of <fo:table-header> or <fo:table-footer> or as a child of <fo:table> at any position where <fo:table-header> or <fo:table-footer> is allowed. <fo:retrieve-table-marker> behaves like <fo:retrieve-marker> but its scope is limited to the <fo:table>. It has properties retrieve-class-name, retrieve-position-within-table, and retrieve-boundary-within-table. <fo:retrieve-table-marker> can retrieve multiple rows (if that is the content of the selected <fo:marker>), and AH Formatter provides the axf:retrieve-table-rows extension property to set the maximum number of retrieved rows.

A table header or footer can contain footnotes. AH Formatter provides the axf:repeat-footnote-in-table-header and axf:repeat-footnote-in-table-footer properties that specify whether footnotes should also be repeated when a table header or footer, respectively, is repeated when the table breaks. The ability to suppress repeated footnotes is not available with CSS.

Breaking tables

AH Formatter also provides the axf:table-row-orphans and axf:table-row-widows extension properties—and -ah-table-row-orphans and -ah-table-row-widows extension CSS properties—that specify the minimum number of rows that must remain at the bottom or top, respectively, of the page (or column) when a table breaks.

For a table cell that breaks across a page or column, AH Formatter provides extensions that either repeat the table cell contents after the break or generate provided content after the break. axf:repeat-cell-content-at-break and -ah-repeat-cell-content-at-break specify whether to generate another copy of the table cell’s content after a break. <axf:table-cell-repeated-marker>, if present in the XSL-FO, provides alternative content that is inserted after a break instead of the second copy of the table cell’s content. In CSS, position: running(table-cell-repeated-marker); on an element in a table cell removes the element from the flow. If its parent table cell breaks, the formatted element is inserted after the break instead of the second copy of the table cell’s contents.

Table caption

Tables can have a caption in both XSL-FO and CSS: in XSL-FO, inside an <fo:table-and-caption> as an <fo:table-caption> that precedes the <fo:table>; in CSS, as an element with display: table-caption; that is the first child of the element for the table.

Column widths

XSL-FO and CSS both define the table-layout property for specifying whether table column widths should be automatically determined from the table’s content or are specified in the table’s markup. AH XSL Formatter is the only XSL formatter that supports automatic table layout, and AH CSS Formatter and the browsers all support automatic table layout.

Table column widths in XSL-FO are specified by the column-width property on <fo:table-column>, and in CSS, by the width property of an element with display: table-column;(and in HTML, the width attribute on <col>).

Both column-width and width can be a length or percentage, but while column-width in XSL specifies a fixed column width, width in CSS specifies a minimum column width.

XSL, but not CSS, also defines the proportional-column-width() function for allocating column widths with fixed table layout: after the fixed components of the column widths are determined, the remainder of the available width is allocated in proportion to the proportional-column-width() values. AH Formatter makes proportional-column-width() available in CSS.

Properties from table columns

Although tables are a grid of rows and columns, the markup for both HTML and XSL-FO tables is ‘row primary’, where table cells are descendants of rows and not of columns. This obviously means that inherited properties cannot ordinarily be inherited from a column definition.

Both XSL and CSS define that border and background properties can apply to cells in the current table column. Border properties from the column definition can apply when border-collapse is collapse (or, in XSL-FO, also collapse-with-precedence).

CSS defines an algorithm for resolving the conflict when multiple border property specifications apply to an edge of a table cell; for example, conflicting border property specifications on the table cell, the table row, and the table column. In essence, the algorithm chooses the most ‘eye catching’ border style unless any of the elements specifies hidden.

XSL adopted the same algorithm for use when border-collapse is separate. When border-collapse is collapse-with-precedence, conflicts are resolved based on the integer precedence value assigned to each FO that can supply the border of a table cell. The default precedence values give priority to a table’s ‘outer’ FOs as well as prioritizing column borders over row borders: <fo:table>, 6; <fo:table-cell>, 5; <fo:table-column>, 4; <fo:table-row>, 3; <fo:table-body>, 2; <fo:table-header>, 1; <fo:table-footer>, 0. However, each table FO can specify a different precedence value for each of the four edges, and can specify force to override all other precedence values.

XSL defines the from-table-column() function that can be used on an <fo:table-cell> or its descendants to retrieve the inherited value of a property as specified on the corresponding <fo:table-column>.

Alignment in table cells

The first line of text in multiple table cells in a table row can have the same baseline in both XSL-FO and CSS, even when text in different cells have different font sizes. For XSL-FO, use relative-align="baseline", and for CSS, use vertical-align: baseline;. CSS defines this behavior for vertical-align only for table cells. Other than on table cells, vertical-align: baseline; in CSS aligns the alphabetic baseline of the element with the alphabetic baseline of its parent element. XSL 1.1 also defines vertical-align, but only as a shorthand for multiple XSL-FO properties and only to match the non-table cell usage in CSS.

Horizontal alignment of text in a table cell is the same in both XSL-FO and CSS when using AH Formatter. XSL 1.1 defined more values for text-align than are defined in CSS2. AH Formatter also implements the XSL 1.1 values for CSS formatting. The CSS Text Module Level 3 defines some different keywords that achieve the same effects as the XSL 1.1 text-align and related properties, except for one difference.

XSL 1.1 (and, consequently, CSS formatting in AH Formatter) allows the value of text-align on descendents of a table cell to be a string. Each of the blocks in one table column that have a string value for text-align will be aligned horizontally so that all of their strings are in the same vertical line. A typical usage is to align all of the numbers in a table column on their decimal point (.) by specifying text-align='"."' or text-align: ".";. AH Formatter also provides the axf:text-align-string and -ah-text-align-string extension properties for specifying the alignment of the aligned strings within their table cells.

Rotated tables and table cells

Entire tables and the content of individual table cells can be rotated both in XSL-FO and in CSS with an AH Formatter extension. In XSL-FO, an <fo:table> can be placed in an <fo:block-container> that specifies the reference-orientation property, and an <fo:table-cell> can contain an <fo:block-container> that specifies the reference-orientation property. In CSS, the -ah-reference-orientation extension property can be specified on both tables and table cells.

Accessibility

The row-and-column grid of a table can be difficult to convey using a screen reader or other assistive technology. For XSL-FO, AH Formatter provides axf:table-summary, axf:headers, and axf:scope extension properties, and for CSS, the corresponding -ah-table-summary, -ah-headers, and -ah-scope properties. These properties bridge between attributes in HTML tables (or other XML markup) and PDF attributes in Tagged PDF and PDF/UA. For XML source that is transformed into XSL-FO, the properties can derive from the source XML or can be added by the XSLT stylesheet.

axf:table-summary and -ah-table-summary correspond to the summary attribute of table in HTML 4.01. (summary was deprecated in HTML5 in favor of caption, even though caption functions like a heading for the table and summary was meant to convey information about the organization of data in the table and to help users navigate the table. [WAI]) axf:table-summary and -ah-table-summary also correspond to the Summary attribute for tables in Tagged PDF and PDF/UA that was introduced in PDF 1.7.

axf:headers and -ah-headers indicate the table head cells that apply to the current table cell. axf:scope and -ah-scope work the other way and indicate whether the current table head cell applies to following cells in the same column, following cells in the same row, or all cells ‘down’ and ‘to the right’ of the current cell.

XSL-FO

XSL defines specialized FOs for representing lists. The FO structure for a two-item list, where indentation represents containment, is:

fo:list-block
  fo:list-item
    fo:list-item-label
      (%block;)+
    fo:list-item-body
      (%block;)+
  fo:list-item
    fo:list-item-label
      (%block;)+
    fo:list-item-body
      (%block;)+

(block;)+ means one or more block-level FOs. This includes <fo:block> and <fo:block-container>, but it also includes, for example, <fo:table> and <fo:list-block>. It is possible to put structured content into an <fo:list-item-label> as well as into an <fo:list-item-body>.

XSL-FO defines the relative-align property for aligning the baselines of the first lines of an <fo:list-item-label> and <fo:list-item-body>.

There is no automatic numbering of list items in XSL-FO. The list item label is expected to be generated by the XSLT transformation. The number could be copied from the source document or it could be generated based either on the structure of the source or on the logic in the stylesheet. XSLT defines a limited number of numbering schemes that can be used to format the list item label. AH Formatter provides the axf:number-transform extension property, which supports more numbering schemes than are provided by XSLT.

axf:number-transform causes the number to which it applies to be formatted as ideographic numerals, as one of the CSS-style counter styles (including symbolic styles), or as one of the styles for the format property. XSL 1.1 defines format as matching the XSLT 1.0 [XSLT10] format attribute, but AH Formatter extends this to support many more numeric, alphabetic, and symbolic sequences.

XSL-FO defines some properties and functions to make it easier to use the same margins for all of the items in the one list. The provisional-label-separation property of <fo:list-block> is part of the formula for label-end(), which is used to determine the end-indent of an <fo:list-item-label>. Similarly, provisional-distance-between-starts is part of the formula for body-start(), which is used to determine the start-indent of an <fo:list-item-body>. The XSL 1.1 Recommendation does not state why ‘provisional’ is included in the properties’ names, but the properties’ values are only one part of each formula. Also, the value of a property where the functions are used can be an expression that adds or subtracts other lengths or even multiplies the function value by some number.

CSS

An element with display: list-item; generates a block box plus a marker box. [CSS3-Display] The same specification also says that the list-item keyword generates a ::marker pseudo-element with the content specified by the ‘list-style’ properties: list-style-type, list-style-position, and list-style-image, with list-style as the shorthand property for all three.

The content of the marker box can be a combination of text and images. More specifically, it is the first of:

• The value of the content property, if that is not normal

  This can be the value of an arbitrary counter that is formatted using any counter style.

• An image generated from list-style-image (followed by a space character)

• String generated from list-style-type

  This can be a literal string or a counter style used for formatting the value of the built-in ‘list-item’ counter.

Otherwise, there is no marker box.

Per-document fonts

CSS defines the @font-face rule that allows the stylesheet to automatically fetch and activate fonts instead of using only the fonts known to the formatter. XSL 1.1 does not define an equivalent feature, but AH Formatter implements the <axf:font-face> extension element for use with XSL-FO.

Links

XSL 1.1 defines <fo:basic-link>, which has separate internal-destination and external-destination properties for referring to IDs within the FO tree and external resources, respectively. One of the properties, but not both, should be specified on an <fo:basic-link>.

<fo:root>, <fo:page-sequence>, <fo:page-sequence-wrapper>, and nearly every FO that can be used within an <fo:page-sequence> can have an id property. <fo:change-bar-begin> and <fo:change-bar-end>, for example, do not have an id property. AH Formatter supports xml:id as an alternative to id on FOs that can have id.

CSS relies on a browser’s implementation of the href attribute of the <a> element to provide linking behavior. The HTML5 specification for a UA stylesheet [WHATWG] does not specify anything for the href attribute. The default html.css file for AH Formatter defines href as setting the -ah-link extension property:

a[href]   { -ah-link: attr(href url); }

-ah-link can similarly be used with other, non-HTML XML vocabularies to generate hyperlinks from other elements or attributes.

Generated text

XSL-FO assumes that references to the number or title of chapters, sections, tables, and figures, etc., will be generated by the XSLT that generated the XSL-FO. The full source document is available to the XSLT processor, and XSLT includes <xsl:number>, which can generate multi-level numbers in a variety of formats. Consequently, XSL-FO does not include a mechanism to copy text from elsewhere in the FO tree.

The only text that XSL-FO can generate is for values that are not known before the document is formatted: page numbers and page number references (and the scaling factor of formatted graphics). <fo:page-number> generates the page number of the current page. <fo:page-number-citation> generates the page number of the page containing the first normal area from the referenced FO, and <fo:page-number-citation-last> generates the page number of the last page of the referenced FO.

AH Formatter extensions for page numbers in XSL-FO include:

• axf:reverse-page-number: page numbers and page number references are counted from the last page of the <fo:page-sequence>
• axf:physical-page-number: generates the physical page number, which will be different from the logical page number if, for example, page numbers restart after the front matter or for each chapter
• axf:origin-id: the generated page number is the difference between the page number of the FO referred to by axf:origin-id and the page number that would ordinarily be generated by the current FO

CSS can generate text based on the content or position of another element in the document. The target-text() function retrieves the text value of a target element or, alternatively, the text value of its ::before or ::after pseudo-element or its first letter. target-counter() (and also target-counters()) retrieves the value of a named counter as seen by a target element. To obtain the page number of a target element, use target-counter() and specify the page counter:

content: target-counter(attr(href url), page);

The AH Formatter extensions for physical and reverse page numbers are available by adding a keyword. For example, to generate the physical page number of a target element:

content: target-counter(attr(href url), page physical);

CSS does not have an equivalent to <fo:page-number-citation-last>.

MathML 3

AH Formatter natively supports MathML 3, whereas browsers and MathJax implement a subset of MathML 2. Improvements between MathML 3 and MathML 2 include:

• Presentation elements for elementary maths layouts

  $$325436.313061210916151.091$$

• Improved linebreaking, spacing adjustment, and directionality control
• <mglyph/> for displaying images of non-standard symbols
• href added to common attributes to allow elements to link to a URI

CSS counters

A CSS counter is a special numeric tracker used, among other things, to automatically number list items in CSS. Counters are created, incremented, or set by specifying CSS properties. There are some predefined counters, such as the page counter for page numbers, that are always present and that are automatically incremented. For example, the page counter is incremented with each new page. The value of a predefined counter can also be modified by setting CSS properties.

Counter styles

CSS supports the following properties on an @counter-style rule, which AH Formatter also supports on <axf:counter-style> in XSL-FO:

• system : Specifies which algorithm to use to construct the counter’s representation.
• negative : Defines how to alter the representation when the value is negative.
• prefix : Specifies a symbol that is prepended to the marker representation.
• suffix : Specifies a suffix that is appended to the marker representation.
• range : Defines the ranges over which the counter style is defined.
• pad : Specifies a symbol with which to pad counter representations that are not a minimum number of grapheme clusters.
• fallback : Fallback counter style to be used when the current counter style cannot create a representation.
• symbols : Symbols to be used by the marker-construction algorithm.
• additive-symbols : Symbols to be used by an additive marker-construction algorithm.
• speak-as : Describes how to synthesize the spoken form of a counter. (Not implemented by AH Formatter.)

The following example shows a ‘my-filled-circled-decimal’ counter style that is a based on the ‘filled-circled-decimal’ counter style from CSS Counter Styles Level 3. [CSS3-CounterStyles] As the name suggests, the counter style uses decimal numbers inside filled circles to represent decimal numbers. The generated symbol is followed by a space.

@counter-style my-filled-circled-decimal {
system: fixed;
         /* Using hex escape of Unicode character codes. */
symbols: '\2776' '\2777' '\2778' '\2779' '\277a' '\277b' '\277c'
         '\277d' '\277e';
/* symbols: '❶' '❷' '❸' '❹' '❺' '❻' '❼' '❽' '❾'; */
suffix: ' ';
}

The XSL-FO equivalent using <axf:counter-style> is:

<axf:counter-style
    name="my-filled-circled-decimal"
    symbols="'❶' '❷' '❸' '❹' '❺' '❻' '❼' '❽' '❾'"
    suffix=" " />

Use axf:number-transform to represent numbers using the counter style:

<fo:list-item-label axf:number-transform="my-filled-circled-decimal">
 <fo:block>1</fo:block>
</fo:list-item-label>

format and related XSL properties

format and its related properties—grouping-separator, grouping-size, letter-value, country, and language—take their definition from the corresponding XSLT 1.0 number-to-string conversion attributes. XSL is defined as both XSLT and XSL-FO, and XSLT 1.0 was the current XSLT version when XSL 1.0 became a Recommendation.

format in XSLT specifies the format of the numbers generated by <xsl:number>. <xsl:number> can generate a list of numbers (when level="multiple"), and the XSLT format attribute contains a sequence of alphanumeric tokens for the format of the potentially multiple levels of number generated by <xsl:number>. These are separated by non-alphanumeric tokens that are repeated as the punctuation between the generated numbers.

format in XSL-FO is just one alphanumeric token that specifies the format for the page number or for the scaling value. <xsl:number> generates only integers, and page numbers are only integers and <fo:scaling-value-citation> generates only an integer percentage value. Any prefix or suffix on a page number is specified with <fo:folio-prefix> or <fo:folio-suffix>, respectively. Using separate FOs for the prefix and suffix allows them to be styled differently from the style for the page number, if desired. Any ‘%’ (or similar) suffix for an <fo:scaling-value-citation> would have to be included in the text of the XSL-FO document.

The number formats defined for format in XSLT are aspirational rather than comprehensive. The format tokens are designed as a superset of the allowed values of the type attribute for the <OL> element in HTML 4.0, but only five token formats are required:

• 1 generates 1 2 ... 10 11 12 ... (and 01 generates 01 02 ... 09 10 11 12 ... 99 100 101 ..., and so on)
  • In principle, any character that has a decimal digit value of 1 (as specified in the Unicode character property database) can be used
• A generates A B C ... Z AA AB AC...
• a generates a b c ... z aa ab ac...
• i generates i ii iii iv v vi vii viii ix x ...
• I generates I II III IV V VI VII VIII IX X ...

Any other character can be used to indicate a numbering sequence, provided that the processor supports it. AH Formatter supports an extensive range of format tokens for numbers in multiple scripts, as well as multiple styles of Roman numerals and even Chinese zodiac signs and the ‘*’, ‘†’, ‘‡’ sequence that is traditionally used for footnotes in English. However, the range is not extensible. If something else is required, you can specify one of the predefined CSS counter styles or specify the name of your own counter style as the value of the format property. For more information, see “format” in the AH Formatter manual.

Rounded corners

CSS 3 provides properties for specifying rounded corners on any element that can have a border. XSL 1.1 does not define equivalent features, but rounded corners are available as an AH Formatter extension.

Multiple background images

XSL 1.1 and CSS 2 support a single background image for a box. CSS 3 allows a box to have multiple background images, which AH Formatter also supports in XSL-FO as an extension.

Background image position

CSS 2 defines the background-position property for specifying the horizontal and vertical position of a background image, or, with CSS 3, background images. XSL 1.1 treats background-position as a shorthand for the separate background-position-horizontal and background-position-vertical properties.

Background image repetition

CSS 2 defines the background-repeat property for specifying whether and how a background image is repeated. CSS 3 defines additional keywords that provide more control over how a repeated image covers the available area.

AH Formatter implements the CSS 3 background-position values for both XSL-FO and CSS and adds a paginate value that is available when embedding a PDF as the background image of a page. Successive pages from the embedded PDF provide the backgrounds of successive pages in the output. The background images can be a subsequence of pages from the embedded PDF. If necessary, extra output pages are generated to match the number of embedded PDF page images.

Bookmarks

XSL 1.1 added <fo:bookmark-tree> and related FOs to hold a list of access points within the document such as a table of contents, a list of figures or tables, etc. The bookmark tree is separate from the visible content of the document. If present, it is a child of <fo:root>, and it appears before the first <fo:page-sequence> (or <fo:page-sequence-wrapper>).

<fo:bookmark-tree> contains one or more <fo:bookmark>. An <fo:bookmark> contains an <fo:bookmark-title> and can also contain any number of subordinate <fo:bookmark>. An <fo:bookmark> can have either an internal-destination property to refer to the ID of an FO in the current document or an <fo:external-destination> to refer to an external resource. The following figure shows a sample bookmark tree structure, where indentation represents containment:

fo:bookmark-tree
  fo:bookmark
    fo:bookmark-title
    fo:bookmark
      fo:title
      fo:bookmark
        fo:bookmark-title
        fo:bookmark
          fo:bookmark-title
    fo:bookmark
      fo:bookmark-title

Because the bookmark tree is separate from the visible content and also because an <fo:bookmark> can refer to any destination, the bookmark tree does not have to represent the exact structure of the document. It is possible, for example, to refer to related documents or web pages from the bookmark tree or it can present multiple views of the document, such as listing sections and also tables in the bookmark tree.

An <fo:bookmark> can be specified as initially showing or hiding its subordinate <fo:bookmark>. An <fo:bookmark-title> can contain text only. Because the bookmark tree is typically generated using XSLT, the text can match the corresponding section title. In some cases, it can be necessary to transform superscript or subscript text into their corresponding plain text form. An <fo:bookmark-title> can have a specified color, its font weight can be normal or bold, and its font style can normal or italic.

Bookmarks in CSS follow the structure of the elements in the document that generate bookmarks. CSS defines an bookmark-level property that applies to all elements. Its value is either none (the default) or an integer, where 1 is the highest level bookmark. The bookmark-label property specifies the text content of the bookmark label. Its initial value is content(text), which generates the text content of the element. The content that can be specified for bookmark-label is the same as for the string-set property: any combination of literal strings, counter values, the content of the current element (or its pseudo-elements), or the value of an attribute of the current element. AH Formatter also allows the -ah-attr-from() and -ah-attr-img() extension functions in bookmark-label.

Bookmarks in CSS automatically link from the bookmark to the element that generated the bookmark. The -ah-outline-internal-destination extension property specifies an ID or a page number (with optional zoom factor) that is used instead of the default link. Alternatively, the -ah-outline-external-destination extension property specifies a URL to use as the link destination.

AH Formatter supports -ah-outline-color, -ah-outline-font-style, and -ah-outline-font-weight extension properties in CSS to provide the same control over the appearance of the bookmark label as is available with XSL-FO.

A block-level element that generates a CSS bookmark label can have a bookmark-state property. When bookmark-state is open, the bookmark label and the bookmark labels of the nearest descendant elements that generate bookmark labels will be shown. Otherwise, the value is closed, and only the bookmark label of the current element is shown.

AH Formatter additionally supports its own extensions for generating bookmarks based on the structure of the document. In general, it is better to use the standard XSL-FO or CSS mechanism instead. The exception is when XSL-FO is formatted to generate multiple PDF volumes. When the AH Formatter extensions are used, a bookmark tree can be generated in the first volume or in each separate volume. The bookmark tree can either cover all the volumes and be the same in each volume or it can cover the current volume only. The AH Formatter extensions include a mechanism for optionally grouping bookmarks. When the bookmark tree is for only the current volume, any bookmark groups in the entire document can appear either in the bookmark tree in the last volume or in the bookmark tree of every volume.

XSL-FO

XSL 1.1 expects that an XSLT transformation will convert index terms in the source XML into index-key properties in the XSL-FO and also sort and collate the index terms to generate the FOs used for formatting the index (or indexes). The bulk of the FOs for a formatted index will be the general-purpose <fo:block>, and so on, for the list of headwords. The page references for each headword are generated from an <fo:index-page-citation-list>. These FOs are also expected to be generated by the XSLT transformation based on the index terms in the source XML. In fact, it is an error if a contained <fo:index-key-reference> does not match any index term in the document.

XSL 1.1 defines multiple FOs for the index reference and, optionally, any prefix or suffix to add to each page number reference. For example, the XSL 1.1 Recommendation shows the example of ‘[’ and ‘]’ around index references to figures. The page numbers, and any prefix or suffix, can be styled using inherited properties such as font-style and font-weight.

There are also properties that specify when and how to merge sequential page numbers and whether to merge page numbers and page ranges across different <fo:index-key-reference>. This controls, for example, whether index references to figures can be merged with ‘ordinary’ index references to the same or adjacent pages. AH Formatter extends the merge-sequential-page-numbers property to allow shorthand notations to be used for two and three successive pages.

CSS

All of the page number references in the index must be included in the document being formatted. Unlike with XSL-FO, there is no facility for generating page number references based on an index key.

AH Formatter provides the -ah-merge-sequential-page-numbers extension property for merging sequential page numbers. When specified on a block-level element, adjacent identical page numbers are merged into one number, and sequences of sequential page numbers are merged into ranges. The page references must be to pages earlier in the document. Generating the shorthand notations for two or three consecutive pages is also possible with CSS.

Suppose the following CSS is specified.

p.index-page-citation-list {
 -ah-merge-sequential-page-numbers: merge;
}
span.index-item {
 content: target-counter(attr(href), page);
}

Then, suppose the following HTML exists.

<p class="index-page-citation-list">
 <span class="index-item" href="#id1"/>,
 <span class="index-item" href="#id2"/>,
 <span class="index-item" href="#id3"/>,
 <span class="index-item" href="#id4"/>,
 <span class="index-item" href="#id5"/>,
 <span class="index-item" href="#id6"/>,
 <span class="index-item" href="#id7"/>,
 <span class="index-item" href="#id8"/>,
 <span class="index-item" href="#id9"/>
</p>

Suppose the page numbers line up as follows:

1, 3, 4, 4, 5, 6, 8, 8, 9

The result will be:

1, 3–6, 8, 9

If -ah-merge-sequential-page-numbers: merge-f; is specified instead, the result will be:

1, 3–6, 8f.

Two-pass formatting

Two-pass formatting is a feature for formatting large documents that is only available for XSL. This is an AH Formatter feature that is outside the scope of either XSL or CSS.

In single-pass formatting, AH Formatter must keep a page in memory until the page numbers of all <fo:page-number-citation> on the page are resolved. All of the following pages are also kept in memory until the page that is the target of the last unresolved <fo:page-number-citation> is formatted.

In two-pass formatting, the first pass resolves and saves the <fo:page-number-citation> values but does not save any formatted pages. In the second pass, AH Formatter immediately resolves every <fo:page-number-citation> using the saved page number information and flushes each page from memory as soon as it is formatted. This allows extremely large documents to be formatted.

Multi-volume output

In XSL formatting but not CSS formatting, a document can be output as multiple PDF files. The bookmarks included in the PDF files can be the same in all volumes or can be different in each volume. The bookmarks in one volume can also refer to IDs in other volumes.

Font configuration

AH Formatter provides extensive control over the fonts that can be used.

The AH Formatter font configuration file specifies:

• Locations of folders containing fonts
• Font files to exclude from use
• Range of Unicode characters to use from a font
• Adjustments to font size, baseline, x-height and other font features
• Aliases that map font names to specific font files

The Option Setting File specifies:

• Mapping of the generic font family names—serif, sans-serif, monospace, cursive and fantasy—to specific fonts for individual scripts
• Whether to emulate italics and small-caps when they are not available in the selected font family
• Fonts to use with MathML

Line numbers

AH Formatter provides extension properties for the display of line numbers. Line numbers can be counted starting from: the current page sequence or a previous page sequence; current page; current column; previous column in the current table; or the current block. The position and appearance of the line number can be specified. The interval between displayed line numbers can be specified, as can a sequence of line numbers that must always be shown.

Line continuation marks

AH Formatter provides extension properties for the display of a mark when a line breaks.

Overprint

You can specify when a color or colors should overprint underlying colors instead of colors that are masked by other colors not printing at all.

Tabs

In XSL-FO but not CSS, it is possible to define horizontal alignment points—similar to tab stops in a word processor. An <axf:tab>, and optionally a tab character (U+0009), aligns its following text on the next tab stop. The start, end, or center of the text, or a decimal point within the text, can be aligned on the tab stop.

Automated analysis

AH Formatter can analyze the formatted text to identify potential typographic problems such as: lines with excessive white-space; rivers of white-space over successive lines; short lines at the end of paragraphs or at the start of a page; consecutive lines starting or ending with the same word; unbalanced spreads; consecutive lines that end with a hyphen; excessive blank pages at the end of the document; and too few lines before or after a block of text.

Automated analysis is quicker and more reliable than visually inspecting every formatted page. However, AH Formatter cannot fix the problems for you. Solving these problems usually requires editorial or stylistic changes, and sometimes both.

Barcode generation

The Barcode Generator Option allows you to embed barcodes, including QR codes, directly in the output as either an SVG or PNG image. Barcode fonts are not required.

<!-- XSL-FO example -->
<fo:external-graphic src="data:application/vnd.ah-barcode;type=QR;
scale=2,Hello%20World!"/>

<!-- HTML example -->
<img src="data:application/vnd.ah-barcode;type=QR;scale=2,
Hello%20World!"/>