SnortValidator is a tool that analyzes snort rules and searches for certain syntactic and semantic errors. It aims to supplement Snort itself, which has a very weak error checking at some points. Hence, SnortValidator detects many things that Snort will silently accept, but that will for sure not work. Additionally, it detects some common semantic problems that indicate wrong usage of keywords that will certainly not do what you actually intended.
If you find a rule example, that Snort accepts but that is either wrong, ambiguous or likely to do something else than intended, please send me an example to decoder@own-hero.net. The same in general also holds for errors that Snort actually detects, but only if the effort required to detect it statically is comparative. Remember that SnortValidator is not meant to replace Snort's checks in general.