SyntacticSemtex is a language syntax feature which, while appealing to experts and gurus for all the power that it gives (for producing short, elegant or obfuscated code, usually) is something that (like real Semtex) allows a novice user to blow his leg off. Or allows the expert/guru user to blow the legs off novice users :P

Contrast SemanticSemtex, which refers to language semantics with unclear confusing effects.

Compare this to SyntacticSugar. SyntacticSugar is generally harmless in small doses; (though if a language definition expands; syntactic sugar which is irregular can cause problems); and usually consists of a shortcut for some language feature. It's primary benefit is expressing a common case or operation more concisely. SyntacticSemtex is SyntacticSugar gone over-board or misused.

Just about any syntax that allows code to be obfuscated (or just obscure, even if not intentionally) could be categorized SyntacticSugar.

A couple from CeeLanguage and CeePlusPlus:
* Braces: allows scope to be changed "sneakily", befuddling the mind of the not-careful-enough reader
* Preprocessor macros: macros are included lexically, and might open/close braces from enclosing code
* Operator overloading: I think this one's more of SemanticSemtex - but still a bit of both. Operator calls are confusing on a syntactic level, hiding the method call actually taking place. The operator *implementation* is potential SemanticSemtex in that it has full power to disregard operator expectations

More general things that'd be SyntacticSemtex in any language:
* Overloaded lexemes: For example, the comma in CeePlusPlus which appears both in argument lists and as the comma operator.
** See OverloadingCommaOperator

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CategoryProgrammingLanguage