It s all down to html s i d There must be only 1 usage of any i d per page Our Headers autocreate ids and just creates a The older html4 method was named anchor links eg which also must be unique per page using name like this is a hack of form submission code iirc To see clearly view source The main reason to care is if on a non wiki website you want to bookmark or link to a place that s partway down Just View Source and look for a i d or name and that stuff that variable after a in the url