Wow
Thanks @btheado This may solve issues I have raised elsewhere, when trying to document and reuse filters, or construct filters.
When used with join it actually is an approach to concatenation and avoids substitution or backtick attributes.
- We may need to document this.
What a trick

\function construct.filter() "[" "length[]match[3]" "prefix[ca]" "]" +[join[]]
<<construct.filter>>
Returns: [length[]match[3]prefix[ca]]
- This may even permit a rewrite of the solution to this topic?
- Note you can even include evaluated filters for variables, fields etc…
[Edited]
If you use <<construct.filter>> as the filter to a list widget it operates as a filter. So it can be viewed or used.
We can say;
- Did you know you can use literals in functions?
- Functions to prepare strings, tooltips and more.
- Functions to generate plain text strings