Function prepend_looseness 

pub fn prepend_looseness(looseness: i32, text: &str) -> String

Prepends \looseness=<looseness> to the provided text.

TeX resets \looseness to zero after every paragraph, so setting it in the preamble only affects the first paragraph. To apply a looseness value to every paragraph, transform each text with this function.

The number is terminated with an empty group rather than a space: otherwise, if the text starts with a space, TeX’s number scanner would consume it and the text would lose its leading interword glue.