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.