On 5/22/2020 19:49, Rik Kabel wrote:
>
> If the OP simply wants the width of a string, one can use 
> \setwidthof#1\to#2.
>
>     \define\String{pqrs}
>     \setwidthof{\String}\to\Wdth
>     \String\ is \Wdth\ wide.
>
>     \setwidthof{{\tfb\em\String}}\to\Wdth
>     {\tfb\em\String} is \Wdth\ wide.
>
> I do not know if that is different from the width of the same string 
> unboxed from the paragraph. There may be some adjustments made in 
> justification, expansion, and such that are not treated.
>
>
Correcting my post (thank you, Floris), the format is a bit different 
than I had written. The following works:

    \starttext
    \define\String{pqrs}
    \setwidthof\String\to\WdthA
    {\String} is \WdthA\ wide.

    \define\String{\tfx\em pqrs}
    \setwidthof\String\to\WdthB
    {\String} is \WdthB\ wide.

    \define\String{\ss pqrs}
    \setwidthof\String\to\WdthC
    {\String} is \WdthC\ wide.
    \stoptext


Giving:

-- 
Rik