Read here:

http://www.unm.edu/~devalenz/handouts/competence.html

http://en.wikipedia.org/wiki/Transformational_grammar

(see section on "Grammatical Theories" there)

Example:
You want to say that "something is strange". There are different ways of saying it with basically the same vocabulary but with more or less slight changes in grammatical structure, e.g.:

(1) This is quite strange.
(2) Seems strange (a so-called ellipitcal sentence with the subject pronoun "it" omitted - always the case in Chinese in such circumstances, there is no equivalent for an "impersonal" it in Chinese as in "It is strange", "it rains", etc.!).
(3) Strange! (exclamation).

.......

Sentence examples (1), (2), (3) are individual ways of saying the same thing on the part of the speaker/writer depending on a number of determining extra-linguistic factors such as situational context, mood, language variety used (formal vs. informal language, registers used, etc.). This is what Chomsky calls "performance". You may also call it less technically "individual style" of expessing yourself.

There is no such thing as a "normative" grammar but this is what your criticism in case of the Turnoi poster may imply.