'Select an appender and append the content to parent.
@param parent: A parent node.
@type parent: L{Element}
@param content: The content to append.
@type content: L{Content}'

def append(self, parent, content):

    appender = self.default
    for a in self.appenders:
        if (a[0] == content.value):
            appender = a[1]
            break
    appender.append(parent, content)
