Is "guideline" actually a synonym for "rule"?
My understanding was that a guideline is a suggestion, but I could certainly be mistaken.
Sources like: thesaurus.com suggest that it is, but some common usage might suggest that it isn't. An example is the scene from Pirates of the Caribean where a character says "... more like guidelines than actual rules."
Note: I'm not suggesting that the language in films is flawless, but rather a possible reflection of how the word is actually used.