The

lang

function returns true or false depending on whether the language of the context node as specified by

xml:lang

attributes is the same as or is a sub-language of the language specified by the argument string. The language of the context node is determined by the value of the

xml:lang

attribute on the context node, or, if the context node has no

xml:lang

attribute, by the value of the

xml:lang

attribute on the nearest ancestor of the context node that has an

xml:lang

attribute. If there is no such attribute, then

lang

returns false. If there is such an attribute, then

lang

returns true if the attribute value is equal to the argument ignoring case, or if there is some suffix starting with - such that the attribute value is equal to the argument ignoring that suffix of the attribute value and ignoring case.