120: Custom mark not declared as link or embedded file

In metadata declarations, a name beginning with an ampersand & refers to a custom mark. The assigned value needs to be a link – either to a local file or a base64-encoded data-URI, that holds the code that the custom mark shall be translated into. Alternatively, the custom mark can be declared with an embedded file as value. Your document uses neither a link nor an embedded file as value.

Solution

Make sure to assign either a link as value by prepending the filename or data URI with an arrow -> in the custom mark declaration as in the following examples:

@ &a: ->/templates/code.html
@ &b: ->data:text/html;base64,PHdicj4=

Or use an embedded file:

@ &c
@ |<wbr>

Note that the custom mark is not succeeded by a colon when an embedded file follows.