Correct:
@charset "iso-8859-7";    PASS

Wrong Capitalization:
@CHARSET "iso-8859-7";    PASS
@ChArSeT "iso-8859-7";    PASS
@cHaRsEt "iso-8859-7";    PASS

Wrong Whitespace:
@charset"iso-8859-7";     PASS
@charset  "iso-8859-7";   PASS
@charset\9"iso-8859-7";   PASS
@charset\A"iso-8859-7";   PASS
@charset\C"iso-8859-7";   PASS
@charset\D"iso-8859-7";   PASS
@charset "iso-8859-7" ;   PASS
 @charset "iso-8859-7";   PASS

Wrong Quote character:
@charset 'iso-8859-7';    PASS
@charset "iso-8859-7';    PASS
@charset 'iso-8859-7";    PASS

Wrong Semicolon:
@charset "iso-8859-7"     PASS