Even though TeX is a single pass compiler, multiple passes can be made by reading a file several times. So I suggest one might consider adding this as a feature of LaTeX3: For example, if one wants to automate the LaTeX standard two-pass compile, the environment "document" data would be put in a special file, which is read twice; if this feature is chosen, the first pass could then be done without actual typesetting, making it faster. Etc. Hans Aberg