The package combines the use of soul with the savepos mechanism
of current pdfTeX so that the user can create (almost)
arbitrary underlining and similar "decorations", including
rules, leaders and even pictures (pgf, pstricks, etc.). Unlike
soul underlines, which are built by repeating small elements,
here each chunk of text to be underlined is a single element.

Homepage:
https://ctan.org/pkg/soulpos
