XDOC is a widget version of DOC_LIBRARY. It is invoked by typing:
IDL> xdoc,'name'
where NAME is the name of the procedure to be examined. The text of the input
procedure will appear in a scroll window, with buttons to control print the
file, and also extracting and copying the file to the current directory as .TXT
file. Calling XDOC without a procedure name will produce a menu listing of all
the directories and/or libraries that are defined in the current IDL_PATH. The
user can subsequently scan the IDL path for any desired procedure by clicking
on a particular path element.