SassVariableNode::isa PHP Method

    public static function isa($token)
    {
        return $token->source[0] === self::SASS_IDENTIFIER || $token->source[0] === self::SCSS_IDENTIFIER;
    }

 /**
  * Creates and returns the next SassNode.
  * The tpye of SassNode depends on the content of the SassToken.
  * @return SassNode a SassNode of the appropriate type. Null when no more
  * source to parse.
  */
 private function getNode($node)
 {
     $token = $this->getToken();
     if (empty($token)) {
         return null;
     }
     switch (true) {
         case SassDirectiveNode::isa($token):
             return $this->parseDirective($token, $node);
             break;
         case SassCommentNode::isa($token):
             return new SassCommentNode($token);
             break;
         case SassVariableNode::isa($token):
             return new SassVariableNode($token);
             break;
         case SassPropertyNode::isa($token, $this->property_syntax):
             return new SassPropertyNode($token, $this->property_syntax);
             break;
         case SassMixinDefinitionNode::isa($token):
             if ($this->syntax === SassFile::SCSS) {
                 throw new SassException('Mixin {which} shortcut not allowed in SCSS', array('{which}' => 'definition'), $this);
             }
             return new SassMixinDefinitionNode($token);
             break;
         case SassMixinNode::isa($token):
             if ($this->syntax === SassFile::SCSS) {
                 throw new SassException('Mixin {which} shortcut not allowed in SCSS', array('{which}' => 'include'), $this);
             }
             return new SassMixinNode($token);
             break;
         default:
             return new SassRuleNode($token);
             break;
     }
     // switch
 }