OmniMark provides several features that allow you to manipulate the attribute values that are a central aspect of SGML and XML. There are two kinds of attributes: element attributes, which are specified in the start tag of an element, and data attributes, which are specified in an external entity declaration.
In general, OmniMark uses the keyword
attribute to refer to element attributes, and
data-attribute to refer to data attributes. There are exceptions to this, as follows:
data-attributesshelf to refer to the selected data attribute
In these cases, either
data-attribute can be used.
The "%v" format item allows you to manipulate or display the attributes of the currently opened element, except when it is used in the body of an
external-data-entity rule, in which case it allows you to access the entity's data attributes.
When you want to access the value of an attribute that belongs to an element or entity reference that is not currently open, the
using prefix can be used.
You can test for the type of attribute or data attribute by using the
attribute is or
data-attribute is test. For example:
attribute foo is name
This test will succeed if that attribute "foo" is of type "name", and fail otherwise. Alternately, you can test whether an attribute or data attribute is not of a specified type:
attribute foo isnt name
If you try to test an attribute or data attribute that isn't declared in the element or entity reference currently being examined, OmniMark will generate an error message and the program will halt. This type of error is easily avoided, however, by using the
is defaulted, or
is implied test. For example, you could use the
is specified test to make sure that attribute "foo" exists prior to testing for its type.
OmniMark also provides two built-in shelves which store all of the declared or specified attributes of an element or external entity. These are the
data-attributes shelves. Note, however, that there are some restrictions on how these shelves can be manipulated.
OmniMark treats list-valued attributes as shelves, also with a variety of restrictions. Where the
attributes shelf allows you to manipulate the values of the various attributes of an element, list-valued attributes can be individually treated as shelves, and the various values of that attribute can be referenced using the
[...] keyword. For example, the following code refers to the third value of the attribute "foo":
The restrictions on how list-valued attributes can be treated as shelves are as follows:
[...]keyword, the entire list of values will be selected as if it were a single string with the individual values separated by a space.
has keytest is not permitted on a list-valued attribute.
Attribute aliases can be defined by the
repeat over action and the
using prefix. An attribute alias serves to simplify attribute identification when more than one opened element has an attribute with the same name.
An attribute alias can be specified for any form of
repeat over loop or
using prefix. Within such a context, the attribute alias name takes precedence over an element attribute or data attribute of the same name. If the alias name happens to be the same as an attribute name, the use of that name always refers to the attribute associated with the alias.
The only time an attribute alias is required is when either
repeat over or
using is used with
specified data-attributes. In these cases, an alias is required so that the selected attribute or attributes can be properly identified within the situation created by the
repeat over loop or
key of indexer is applied in these situations, the real name of the attribute is returned, not the alias name.
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