code: func (v *evalVisitor) findBlockParam(node *ast.PathExpression) (string, interface{}) {
  	if len(node.Parts) > 0 {
  		name := node.Parts[0]
  		if value := v.blockParam(name); value != nil {
  			return name, value
  		}
  	}
  
  	return "", nil
  }
docs: // findBlockParam returns node's block parameter