built-in shelf
A built-in variable 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-translation or context-translation is being done, 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.