Module helpers 

Functions

preceding_para_sibling

Does an ltx:para element immediately precede node? Both prune_empty_para (to decide ltx_pruned_first) and the first-paragraph ltx_noindent stamp (tex_paragraph.rs, OXIDIZED_DESIGN #143) ask this: a paragraph with no preceding ltx:para sibling is the first paragraph of its parent, structurally — a signal robust to how many stray \pars fired before it (which varies by TeX Live year / dump vs no-dump).

prune_empty_para

In some cases we could have e.g. a \noindent followed by a {table}, in which case we end up with an empty ltx:para which we can prune.