go to Editor XMLDB and edit one of the Moodle tables.
When you are in front to the list of the fields of a table, just click on one field's name. You get a blank page.

Just an example: I am editing the table "data_fields" of mod/data/db.
By clicking the link on the field name "param3" I get a blank page at the address:

http://localhost:8888/moodle19/admin/xmldb/index.php?action=view_field_xml&dir=%2Fmod%2Fdata%2Fdb&field=param3&table=data_fields&select=edited