Filtered attribute values are indicated with triple curly braces around a Filter Expression. The value will be the first item in the resulting list, or the empty string if the list is empty.

Depuis : 5.2.2 To improve readability, newlines can be included anywhere that whitespace is allowed within filtered attributes.

This example shows how to add a prefix to a value:

<$text text={{{ [<currentTiddler>addprefix[$:/myprefix/]] }}} />