where charset_to and charset_from are expressions. For example:

CONVERT('test','latin2','cp1250')


sql/item_strfunc.cc:
  Now this syntax works too:  CONVERT(string,charset_to,charset_from)
sql/item_strfunc.h:
  Now this syntax works too:  CONVERT(string,charset_to,charset_from)
sql/sql_yacc.yy:
  Now this syntax works too:  CONVERT(string,charset_to,charset_from)