Chapter 21. Macros

Macros are a mechanism for substituting parametrized text into output documents.

Macros have a name, a single target argument and an attribute list. The usual syntax is <name>:<target>[<attrlist>] (for inline macros) and <name>::<target>[<attrlist>] (for block macros). Here are some examples:

http://www.docbook.org/[DocBook.org]
include::chapt1.txt[tabsize=2]
mailto:srackham@gmail.com[]

Macro behavior

21.1. Inline Macros

Inline Macros occur in an inline element context. Predefined Inline macros include URLs, image and link macros.

21.1.1. URLs

http, https, ftp, file, mailto and callto URLs are rendered using predefined inline macros.

  • If you don’t need a custom link caption you can enter the http, https, ftp, file URLs and email addresses without any special macro syntax.
  • If the <attrlist> is empty the URL is displayed.

Here are some examples:

http://www.docbook.org/[DocBook.org]
http://www.docbook.org/
mailto:joe.bloggs@foobar.com[email Joe Bloggs]
joe.bloggs@foobar.com

Which are rendered:

DocBook.org

http://www.docbook.org/

email Joe Bloggs

joe.bloggs@foobar.com

If the <target> necessitates space characters use %20, for example large%20image.png.

21.1.2. Internal Cross References

Two AsciiDoc inline macros are provided for creating hypertext links within an AsciiDoc document. You can use either the standard macro syntax or the (preferred) alternative.

anchor

Used to specify hypertext link targets:

[[<id>,<xreflabel>]]
anchor:<id>[<xreflabel>]

The <id> is a unique string that conforms to the output markup’s anchor syntax. The optional <xreflabel> is the text to be displayed by captionless xref macros that refer to this anchor. The optional <xreflabel> is only really useful when generating DocBook output. Example anchor:

[[X1]]

You may have noticed that the syntax of this inline element is the same as that of the BlockId block element, this is no coincidence since they are functionally equivalent.

xref

Creates a hypertext link to a document anchor.

<<<id>,<caption>>>
xref:<id>[<caption>]

The <id> refers to an anchor ID. The optional <caption> is the link’s displayed text. Example:

<<X21,attribute lists>>

If <caption> is not specified then the displayed text is auto-generated:

  • The AsciiDoc xhtml11 and html5 backends display the <id> enclosed in square brackets.
  • If DocBook is produced the DocBook toolchain is responsible for the displayed text which will normally be the referenced figure, table or section title number followed by the element’s title text.

Here is an example:

[[tiger_image]]
.Tyger tyger
image::tiger.png[]

This can be seen in <<tiger_image>>.

21.1.3. Linking to Local Documents

Hypertext links to files on the local file system are specified using the link inline macro.

link:<target>[<caption>]

The link macro generates relative URLs. The link macro <target> is the target file name (relative to the file system location of the referring document). The optional <caption> is the link’s displayed text. If <caption> is not specified then <target> is displayed. Example:

link:downloads/foo.zip[download foo.zip]

You can use the <filename>#<id> syntax to refer to an anchor within a target document but this usually only makes sense when targeting HTML documents.

21.1.4. Images

Inline images are inserted into the output document using the image macro. The inline syntax is:

image:<target>[<attributes>]

The contents of the image file <target> is displayed. To display the image its file format must be supported by the target backend application. HTML and DocBook applications normally support PNG or JPG files.

<target> file name paths are relative to the location of the referring document.

Image macro attributes

  • The optional alt attribute is also the first positional attribute, it specifies alternative text which is displayed if the output application is unable to display the image file (see also Use of ALT texts in IMGs). For example:

    image:images/logo.png[Company Logo]
  • The optional title attribute provides a title for the image. The block image macro renders the title alongside the image. The inline image macro displays the title as a popup “tooltip” in visual browsers (AsciiDoc HTML outputs only).
  • The optional width and height attributes scale the image size and can be used in any combination. The units are pixels. The following example scales the previous example to a height of 32 pixels:

    image:images/logo.png["Company Logo",height=32]
  • The optional link attribute is used to link the image to an external document. The following example links a screenshot thumbnail to a full size version:

    image:screen-thumbnail.png[height=32,link="screen.png"]
  • The optional scaledwidth attribute is only used in DocBook block images (specifically for PDF documents). The following example scales the images to 75% of the available print width:

    image::images/logo.png[scaledwidth="75%",alt="Company Logo"]
  • The image scale attribute sets the DocBook imagedata element scale attribute.
  • The optional align attribute aligns block macro images horizontally. Allowed values are center, left and right. For example:

    image::images/tiger.png["Tiger image",align="left"]
  • The optional float attribute floats the image left or right on the page (works with HTML outputs only, has no effect on DocBook outputs). float and align attributes are mutually exclusive. Use the unfloat::[] block macro to stop floating.

21.1.5. Comment Lines

See comment block macro.

21.2. Block Macros

A Block macro reference must be contained in a single line separated either side by a blank line or a block delimiter.

Block macros behave just like Inline macros, with the following differences:

  • They occur in a block context.
  • The default syntax is <name>::<target>[<attrlist>] (two colons, not one).
  • Markup template section names end in -blockmacro instead of -inlinemacro.

21.2.1. Block Identifier

The Block Identifier macro sets the id attribute and has the same syntax as the anchor inline macro since it performs essentially the same function — block templates use the id attribute as a block element ID. For example:

[[X30]]

This is equivalent to the [id="X30"] AttributeList element).

21.2.2. Images

The image block macro is used to display images in a block context. The syntax is:

image::<target>[<attributes>]

The block image macro has the same macro attributes as it’s inline image macro counterpart.

Block images can be titled by preceding the image macro with a BlockTitle. DocBook toolchains normally number titled block images and optionally list them in an automatically generated List of Figures backmatter section.

This example:

.Main circuit board
image::images/layout.png[J14P main circuit board]

is equivalent to:

image::images/layout.png["J14P main circuit board",
                          title="Main circuit board"]

A title prefix that can be inserted with the caption attribute (HTML backends). For example:

.Main circuit board
[caption="Figure 2: "]
image::images/layout.png[J14P main circuit board]

21.2.3. Comment Lines

Single lines starting with two forward slashes hard up against the left margin are treated as comments. Comment lines do not appear in the output unless the showcomments attribute is defined. Comment lines have been implemented as both block and inline macros so a comment line can appear as a stand-alone block or within block elements that support inline macro expansion. Example comment line:

// This is a comment.

If the showcomments attribute is defined comment lines are written to the output:

  • In DocBook the comment lines are enclosed by the remark element (which may or may not be rendered by your toolchain).
  • The showcomments attribute does not expose Comment Blocks. Comment Blocks are never passed to the output.

21.3. System Macros

System macros are block macros that perform a predefined task and are hardwired into the asciidoc(1) program.

  • You can escape system macros with a leading backslash character (as you can with other macros).
  • The syntax and tasks performed by system macros is built into asciidoc(1) so they don’t appear in configuration files. You can however customize the syntax by adding entries to a configuration file [macros] section.

21.3.1. Include Macros

The include and include1 system macros to include the contents of a named file into the source document.

The include macro includes a file as if it were part of the parent document — tabs are expanded and system macros processed. The contents of include1 files are not subject to tab expansion or system macro processing nor are attribute or lower priority substitutions performed. The include1 macro’s intended use is to include verbatim embedded CSS or scripts into configuration file headers. Example:

include::chapter1.txt[tabsize=4]

Include macro behavior

  • If the included file name is specified with a relative path then the path is relative to the location of the referring document.
  • Include macros can appear inside configuration files.
  • Files included from within DelimitedBlocks are read to completion to avoid false end-of-block underline termination.
  • Attribute references are expanded inside the include target; if an attribute is undefined then the included file is silently skipped.
  • The tabsize macro attribute sets the number of space characters to be used for tab expansion in the included file (not applicable to include1 macro).
  • The depth macro attribute sets the maximum permitted number of subsequent nested includes (not applicable to include1 macro which does not process nested includes). Setting depth to 1 disables nesting inside the included file. By default, nesting is limited to a depth of ten.
  • If the he warnings attribute is set to False (or any other Python literal that evaluates to boolean false) then no warning message is printed if the included file does not exist. By default warnings are enabled.
  • Internally the include1 macro is translated to the include1 system attribute which means it must be evaluated in a region where attribute substitution is enabled. To inhibit nested substitution in included files it is preferable to use the include macro and set the attribute depth=1.

21.3.2. Conditional Inclusion Macros

Lines of text in the source document can be selectively included or excluded from processing based on the existence (or not) of a document attribute.

Document text between the ifdef and endif macros is included if a document attribute is defined:

ifdef::<attribute>[]
:
endif::<attribute>[]

Document text between the ifndef and endif macros is not included if a document attribute is defined:

ifndef::<attribute>[]
:
endif::<attribute>[]

<attribute> is an attribute name which is optional in the trailing endif macro.

If you only want to process a single line of text then the text can be put inside the square brackets and the endif macro omitted, for example:

ifdef::revnumber[Version number 42]

Is equivalent to:

ifdef::revnumber[]
Version number 42
endif::revnumber[]

ifdef and ifndef macros also accept multiple attribute names:

  • Multiple , separated attribute names evaluate to defined if one or more of the attributes is defined, otherwise it’s value is undefined.
  • Multiple + separated attribute names evaluate to defined if all of the attributes is defined, otherwise it’s value is undefined.

Document text between the ifeval and endif macros is included if the Python expression inside the square brackets is true. Example:

ifeval::[{rs458}==2]
:
endif::[]
  • Document attribute references are expanded before the expression is evaluated.
  • If an attribute reference is undefined then the expression is considered false.

Take a look at the *.conf configuration files in the AsciiDoc distribution for examples of conditional inclusion macro usage.

21.3.3. Executable system macros

The eval, sys and sys2 block macros exhibit the same behavior as their same named system attribute references. The difference is that system macros occur in a block macro context whereas system attributes are confined to inline contexts where attribute substitution is enabled.

The following example displays a long directory listing inside a literal block:

------------------
sys::[ls -l *.txt]
------------------
[Note]

There are no block macro versions of the eval3 and sys3 system attributes.

21.3.4. Template System Macro

The template block macro allows the inclusion of one configuration file template section within another. The following example includes the [admonitionblock] section in the [admonitionparagraph] section:

[admonitionparagraph]
template::[admonitionblock]

Template macro behavior

  • The template::[] macro is useful for factoring configuration file markup.
  • template::[] macros cannot be nested.
  • template::[] macro expansion is applied after all configuration files have been read.

21.4. Passthrough macros

Passthrough macros are analogous to passthrough blocks and are used to pass text directly to the output. The substitution performed on the text is determined by the macro definition but can be overridden by the <subslist>. The usual syntax is <name>:<subslist>[<passtext>] (for inline macros) and <name>::<subslist>[<passtext>] (for block macros). Passthroughs, by definition, take precedence over all other text substitutions.

pass

Inline and block. Passes text unmodified (apart from explicitly specified substitutions). Examples:

pass:[<q>To be or not to be</q>]
pass:attributes,quotes[<u>the '{author}'</u>]
asciimath, latexmath
Inline and block. Passes text unmodified. Used for mathematical formulas.
+++

Inline and block. The triple-plus passthrough is functionally identical to the pass macro but you don’t have to escape ] characters and you can prefix with quoted attributes in the inline version. Example:

Red [red]+++`sum_(i=1)\^n i=(n(n+1))/2`$+++ AsciiMathML formula
$$

Inline and block. The double-dollar passthrough is functionally identical to the triple-plus passthrough with one exception: special characters are escaped. Example:

$$`[[a,b],[c,d]]((n),(k))`$$
`
Text quoted with single backtick characters constitutes an inline literal passthrough. The enclosed text is rendered in a monospaced font and is only subject to special character substitution. This makes sense since monospace text is usually intended to be rendered literally and often contains characters that would otherwise have to be escaped. If you need monospaced text containing inline substitutions use a plus character instead of a backtick.

21.5. Macro Definitions

Each entry in the configuration [macros] section is a macro definition which can take one of the following forms:

<pattern>=<name>[<subslist]
Inline macro definition.
<pattern>=#<name>[<subslist]
Block macro definition.
<pattern>=+<name>[<subslist]
System macro definition.
<pattern>
Delete the existing macro with this <pattern>.

<pattern> is a Python regular expression and <name> is the name of a markup template. If <name> is omitted then it is the value of the regular expression match group named name. The optional [<subslist] is a comma-separated list of substitution names enclosed in [] brackets, it sets the default substitutions for passthrough text, if omitted then no passthrough substitutions are performed.

Pattern named groups. The following named groups can be used in macro <pattern> regular expressions and are available as markup template attributes:

name
The macro name.
target
The macro target.
attrlist
The macro attribute list.
passtext
Contents of this group are passed unmodified to the output subject only to subslist substitutions.
subslist
Processed as a comma-separated list of substitution names for passtext substitution, overrides the the macro definition subslist.

Here’s what happens during macro substitution

  • Each contextually relevant macro pattern from the [macros] section is matched against the input source line.
  • If a match is found the text to be substituted is loaded from a configuration markup template section named like <name>-inlinemacro or <name>-blockmacro (depending on the macro type).
  • Global and macro attribute list attributes are substituted in the macro’s markup template.
  • The substituted template replaces the macro reference in the output document.