XML in a Nutshell, 3rd Edition

#PCDATA

The simplest content specification is one that says an element may only contain parsed character data, but may not contain any child elements of any type. In this case the content specification consists of the keyword #PCDATA inside parentheses. For example, this declaration says that a phone_number element may contain text but may not contain elements:

<!ELEMENT phone_number (#PCDATA)>

Such an element may also contain character references and CDATA sections (which are always parsed into pure text) and comments, and processing instructions (which don’t really count in validation). It may contain entity references only if those entity references resolve to plain text without any child elements.