operator
attribute attribute-name (of element-expression)? indexer
You can access the value of an XML or SGML attribute using the attribute operator.
Attribute references are always treated as string expressions, even if the attribute was declared in the SGML document to be of type NUMBER. However, string expressions which contain a valid representation of a decimal number can be used anywhere where a numeric expression is permitted, so this interpretation places no restriction on the use of attributes.
Attributes can always be further identified by following the attribute name with an element qualifier.
Within the external-data-entity rule, unqualified attributes are data attributes; in other
contexts, they are attributes of the current element.
An item-based indexer can be used if the attribute was declared as a list-valued attribute. However,
unlike shelves, for which the lastmost value is selected unless indicated otherwise, attributes do not
have a default selected value: if no indexer is specified, the whole attribute value is either tested
or is output as a single unit.
Attribute references provide the attribute value unmodified, except for:
delimiter declaration (which is, by
default, a single space) to separate the tokens of a list-value attribute.
In particular, translate rule processing is not performed on the value of an attribute when it is
referenced using the attribute herald. This contrasts with references to an attribute value using
the "%v" modifier.
Attempting to access an attribute will cause an error:
#implied,
#required or #current (and no previous occurrence of an element named in the same
declaration gave the attribute a value).
When using an element-expression the programmer should be aware that:
of element qualifier is usually not needed, since, in most contexts, unqualified
attributes are assumed to be attributes of the current element. In external-data-entity
rules, however, attributes by default are assumed to be data attributes. In that context, the of
element qualifier is significant.
of ancestor, of preparent and of open element qualifiers
refer to the specified ancestor that was most recently opened (the one the fewest "generations" removed from
the current element).
of ancestor, of preparent and of open element qualifiers can
list several element names.
In the header and body of an external-data-entity rule, all unqualified references to attributes
actually refer to data attributes of the external entity being processed. In all other rules, they refer to
element attributes (attributes of element start tags).
Unqualified references to attributes inside functions always refer to element attributes. In order to refer to
the data attributes of an external entity being processed, the qualifier of entity must be
specified.
Element qualifiers can themselves be qualified.
This sample shows how the of ancestor qualifier can list several element names. Note that of
preparent and of open element can also be used to perform this function.
attribute "indent" of ancestor ("numlist" | "bullist" | "deflist")
Specifically, this line of code refers to the indent attribute of a containing
numlist, bullist, or deflist, whichever comes first, searching outwards
from the current element. Note that an error would result if the first element encountered did not have a value
specified for the indent attribute.
The following example illustrates how element qualifiers can be used with attribute references. By using the
element qualifier of ancestor, this line of code refers to the date attribute of an
enclosing element whose name is change.
attribute "date" of ancestor "change"