[Solved] Are there any file naming rules to save ampersand prefixed units?

[PascalDragon]

In fact the route for the FPC distribution is towards a variant with dotted unit names more compatible to current Delphi versions.

On that note, it is sometimes confusing what names are and aren't allowed. imho A name is a name (including the dot) so when I name my unit class.custom (or custom.class) I more or less expect the compiler to not complain about expecting an identifier.

If you're using language keywords then those aren't considered valid identifiers unless prefixed with &. In addition to that some keywords are context sensitive.