Name question in macros

is there a listing of the rules about what names can be used for icons and attributes which are going to be used in macros and their values? A friend has had several macros fail till he changed character names, (some too long, some to short?) Is there min/max length or restricted terms for names? Also I've experienced a difficulties on a couple of macro's giving errors when they reference an unused |max value. The error was fixed as soon as I put anything in the referenced cell. Is this a rule I haven't seen listed anywhere, in the first attribute cell a null or 0 is assumed if its empty and doesn't break the macro.

I have not seen any names fail. If you can provide examples for testing that would be helpful.

Before Rugged Reroll, I saw this issue on occasion; specifically, I noted that any attribute or ability which had a space in its name would not work properly when called by another ability or macro. Example: Hit_Points would not work; HitPoints would. Cure_Light_Wounds would not work; CureLightWounds would. I changed all my information since Rugged Reroll so I no longer have this problem; whether it's still a 'problem' at all I couldn't say for sure.

Ok, in my testing Attributes using a _ or a space work fine. Abilities and macros cannot have spaces (they are not supposed to). Spaces are replaced with a dash. If you can replicate the problem please send me the steps. :)