def as_method(value)
      case true
      when value.tag?
        @methods_from_names[element(value).name]
      when value.dicom_name?
        @methods_from_names[value]
      when value.dicom_method?
        @names_from_methods.has_key?(value.to_sym) ? value.to_sym : nil
      else
        nil
      end
    end
def as_method(value)
      case true
      when value.tag?
        @methods_from_names[element(value).name]
      when value.dicom_name?
        @methods_from_names[value]
      when value.dicom_method?
        @names_from_methods.has_key?(value.to_sym) ? value.to_sym : nil
      else
        nil
      end
    end
Gives the method (symbol) corresponding to the specified element string value.

 @param [String] value an element tag, element name or an element's method name
 @return [Symbol, NilClass] the matched element method, or nil if no match is made