The tt(ERROR) macro takes one argument: text to display to the standard error
stream. The current input file and line number are also displayed. After
displaying the text, the tt(yodl) program aborts with an exit status of 1.

This command can be used, e.g., in a macro package when an incorrect macro is
expanded. In my macro package (see chapter ref(macropackage)) the tt(ERROR)
macro is used when the sectioning command tt(chapter()) is used in an
tt(article) document (in the package, tt(chapter)'s are only available in
tt(book)s or tt(report)s).

An analogous builtin macro is tt(WARNING), which also prints a message but 
does not exit (see section ref(warning)).
