A third numeric argument targets a particular position in the string. An optional fourth argument specifies the number of characters to select. If the first string argument in the node test is the empty string, then relevant positions in the context node's text contents will be selected. For another example, let's suppose you want to find the year of birth for all people born in the nineteenth century. When matching strings, case is considered.
All white space is condensed to a single space.
Markup characters are ignored.