A bit hacky way to identify invalid CSS property definition: when user
starts writing new abbreviation in CSS rule, he actually creates invalid
CSS property definition and this method tries to identify such abbreviation
and prevent it from being added to CSS edit tree
@param {TokenIterator} it
function isValidIdentifier(it) {
//		return true;
		var tokens = it.tokens;
		for (var i = it._i + 1, il = tokens.length; i < il; i++) {
			if (tokens[i].type == ':')
				return true;
			
			if (tokens[i].type == 'identifier' || tokens[i].type == 'line')
				return false;
		}
		
		return false;
	}