built-in shelf
#line-number is a built-in shelf that provides the number of the line in which a markup error
occurred. (This is the line number in the markup file, as seen by the parser.) #line-number can be
accessed only from the header and body of markup-error rules.
If an up-translate or context-translate is being executed, the line number is based on the
lines of output from find, find-start, find-end
and external-text-entity rules sent to the parser.