You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
99 lines
4.2 KiB
99 lines
4.2 KiB
////
|
|
Included in:
|
|
|
|
- user-manual: Attributes
|
|
////
|
|
|
|
// tag::intro[]
|
|
Attributes are one of the features that sets Asciidoctor apart from other lightweight markup languages.
|
|
Attributes can activate features (behaviors, styles, integrations, etc) or hold replacement (i.e., variable) content.
|
|
|
|
In Asciidoctor, attributes are classified as:
|
|
|
|
* <<env-attributes,Environment attributes>>
|
|
* <<builtin-attributes,Built-in attributes>>
|
|
* <<charref-attributes,Predefined attributes>>
|
|
* <<glossary,User-defined attributes>>
|
|
* <<attribute-assignment-precedence,API and Command Line Attributes>>
|
|
* <<setting-attributes-on-an-element,Element Attributes>>
|
|
// end::intro[]
|
|
|
|
// tag::attributesyntax[]
|
|
=== Attribute Restrictions
|
|
|
|
All attributes have a name and a value (though the value may be implicit).
|
|
|
|
The attribute name:
|
|
|
|
* must be at least one character long,
|
|
* must begin with a word character (A-Z, a-z, 0-9 or _) and
|
|
* must only contain word characters and hyphens.
|
|
|
|
In other words, the name cannot contain dots or spaces.
|
|
|
|
Although uppercase characters are permitted in an attribute entry (the place where an attribute is defined), the attribute name is converted to lowercase before being stored.
|
|
The attribute name in an attribute reference is also converted to lowercase before the attribute is resolved.
|
|
For example, `URI`, `Uri` and `uRI` are all treated as `uri`.
|
|
(See https://github.com/asciidoctor/asciidoctor/issues/509[issue #509] for a proposed change to this restriction).
|
|
A best practice is to only use lowercase for letters in the name and avoid starting the name with a number.
|
|
|
|
The attribute value:
|
|
|
|
* can be any inline content and
|
|
* can only contain line breaks if an explicit line continuation is used.
|
|
|
|
Certain attributes have a restricted range of allowable values.
|
|
See the entries in the <<attribute-catalog>> for details.
|
|
// end::attributesyntax[]
|
|
|
|
=== Attribute Assignment Precedence
|
|
// tag::order[]
|
|
The attribute assignment precedence, listed from highest to lowest, is as follows:
|
|
|
|
* An attribute defined using the API or CLI
|
|
* An attribute defined in the document
|
|
* The default value of the attribute, if applicable
|
|
|
|
Let's use the `imagesdir` attribute to show how precedence works.
|
|
|
|
The default value for the `imagesdir` attribute is an empty string.
|
|
Therefore, if the `imagesdir` attribute is not assigned a value (either in the document, API, or CLI), the processor will assign it the default value of empty string.
|
|
If the `imagesdir` attribute is set in the document (meaning assigned a new value, such as `images`), that value will override the default value.
|
|
Finally, if a value is assigned to the `imagesdir` attribute via the API or CLI, that value will override both the default value and the value assigned in the document.
|
|
|
|
It's possible to alter this order of precedence using a modifier, covered in the next section.
|
|
|
|
==== Altering the Attribute Assignment Precedence
|
|
|
|
You can allow the document to reassign an attribute that is defined via the API or CLI by adding the `@` precedence modifier to the end of the attribute value (or, since 1.5.7, the end of the attribute name).
|
|
Adding this modifier lowers the precedence so that an assignment in the document still wins out.
|
|
We sometimes refer to this as "`soft setting`" the attribute.
|
|
This feature can be useful for assigning default values for attribute, but still letting the document control its own fate.
|
|
|
|
NOTE: The `@` modifier is removed before the assignment is made.
|
|
|
|
Here's an example that shows how to set the `imagesdir` from the CLI with a lower precedence:
|
|
|
|
$ asciidoctor -a imagesdir=images@ doc.adoc
|
|
|
|
Since 1.5.7, you can place the modifier at the end of the attribute name:
|
|
|
|
$ asciidoctor -a imagesdir@=images doc.adoc
|
|
|
|
It's now possible to override the value of the `imagesdir` attribute from within the document:
|
|
|
|
[source,asciidoc]
|
|
----
|
|
= Document Title
|
|
:imagesdir: new/path/to/images
|
|
----
|
|
|
|
Let's update the attribute assignment precedence list defined earlier to reflect this additional rule:
|
|
|
|
* An attribute passed to the API or CLI
|
|
* An attribute defined in the document
|
|
* An attribute passed to the API or CLI whose value (or, since 1.5.7, name) ends in `@`
|
|
* The default value of the attribute, if applicable
|
|
|
|
Regardless of whether the precedence modifier is applied, an attribute assignment always overrides the default value.
|
|
// end::order[]
|
|
|