Where the payload being fastened needs top-level child elements of the stanza holding the fastening (e.g. if a message edit uses the top-level <body> child), these can be listed in <external> child elements of the <apply-to> element, in the same namespace. An <external> element has two attributes: the 'name' attribute MUST be included, and is the name of the top-level stanza child element; the 'element-namespace' attribute specifies the namespace of the element, or if absent indicates that the element is in the same namespace as the stanza (eliding the stream namespace in this way avoids issues when transporting fastenings across combinations of 'jabber:server' and 'jabber:client' streams.
If "user2@chatservice.example" wanted to send an edit (using a fictional protocol) of a message they previously sent with origin-id 'origin-id-2', and the edit protocol used top-level <body> and <custom> elements, it would look like this.
When an entity wishes to replace a fastening they have previously applied it does this by including an attribute 'replace' with value 'true' on the <apply-to> element. The child payload of the <apply-to> element then logically replaces a fastening previously applied by the sending entity with the same name and namespace.
For example, if user2 wished to update the fastening from the first example they would send: