[sitkack]

> - What would you do with code comments? Things like "f(/+old_value+/new_value)".

Comments are included in the AST, the AST should be reprojectable into canonical plaint text.

> - How to store code before preprocessing (C and C++) ?

This could get tricky, punt. cdata

> - How to store files mixing several languages (PHP, HTML, Javascript) ?

Same file format, different semantics. PHP is a DSL.

My new language manifesto includes having a mandatory publicly defined AST.

[marssaxman]

If it is reprojectable into canonical plain text, it's not really an AST - just an ST.