Description
[common] handle character data.
Following http://wiki.tei-c.org/index.php/XML_Whitespace#XSLT_Normalization_Code,
the algorithm to normalize space in mixed content is:
Collapse all white space, then
trim leading space on the first text node in an element and
trim trailing space on the last text node in an element,
trim both if a text node is both first and last, i.e., is the only text node in the
element.