text under barline

[Felipe Gasper]

Hello,

        I’m converting some Gregorian chant scores from GABC to Lilypond. I’m 
looking for a way to put a bit of italicized text (e.g., “Ps.”) under a 
barline, as is typical with some chant genres.

        You can see an example here, on the 3rd line: 
https://gregobase.selapa.net/chant_img.php?id=1123

        Does anyone know of a way to do this with Lilypond?

        Thank you!

cheers,
-Felipe Gasper