Creates a ValueElement instance from the specified <parameter> XML tag.

def _parse_parameter(tag, parser, parent):
    """Creates a ValueElement instance from the specified <parameter> XML tag."""
    name, modifiers, dtype, kind = _parse_common(tag)
    if "default" in tag.attrib:
        default = tag.attrib["default"]
    else:
        default = None
    if "dimension" in tag.attrib:
        dimension = tag.attrib["dimension"]
    else:
        dimension = None

    result = ValueElement(name, modifiers, dtype, kind, default, dimension, parent)
    doc = DocElement(tag, parser, result)
    result.docstring.append(doc)
    parent.add_parameter(result)