This doesn't work as desired.

$ printf ".device ps:exec 7:device [/Dest /pdf:bm1 /Title (Eat at Joe's Caf\\[e aa].) /Level 1 /OUT pdfmark\n" | ./build/test-groff -T pdf -Z | grep '^x X'
troff:<standard input>:1: error: composite special character escape sequences not yet supported in device extension command arguments
x X ps:exec 7:device [/Dest /pdf:bm1 /Title (Eat at Joe's Caf\[e aa].) /Level 1 /OUT pdfmark

What I want is the same result as if I use the `\X` escape sequence.

$ printf "\X@ps:exec 7:device [/Dest /pdf:bm1 /Title (Eat at Joe's Caf\\[e aa].) /Level 1 /OUT pdfmark@\n" | ./build/test-groff -T pdf -Z | grep '^x X'
x X ps:exec 7:device [/Dest /pdf:bm1 /Title (Eat at Joe's Caf\[u00E9].) /Level 1 /OUT pdfmark

Observe how `\[e aa]` gets translated to `\[u00E9]`.