Parses <Constant>

        @param node: Node containing the <Constant> element
        @type node: xml.etree.Element

def parse_constant(self, node):
        """
        Parses <Constant>

        @param node: Node containing the <Constant> element
        @type node: xml.etree.Element
        """

        try:
            name = node.lattrib['name']
        except:
            self.raise_error('<Constant> must specify a name.')

        dimension = node.lattrib.get('dimension', None)

        try:
            value = node.lattrib['value']
        except:
            self.raise_error("Constant '{0}' must have a value.", name)

        description = node.lattrib.get('description', '')

        constant = Constant(name, value, dimension, description)

        if self.current_component_type:
            self.current_component_type.add_constant(constant)
        else:
            self.model.add_constant(constant)