Why a user can "modify" but not "save" a document?

I am just starting using users and I create a group that can MODIFY the content of a page, but not SAVE it... what does it means? It happends that he can start the FCKEditor, but when he tries to save his changes, it doesn’t work (and it does not display any message)... turning on the "save" feature make it all work properly

I think that actually means that the user can view the code for the document, but cannot save it unless he also has "save" permissions.

to see the document source, you can use the browser facilities...

Well, that won’t show what snippets, chunks, TVs etc are being used.