#!/bin/sh
awk -v u="12_3" - <<-'FIN'
BEGIN {
	v = "";

	while (match(u, /\\.|_/)) {
		m = substr(u, RSTART, RLENGTH);
		v = v substr(u, 1, RSTART - 1) (m == "_" ? " " : substr(m, 2));
		u = substr(u, RSTART + RLENGTH);
	}

	v = v u;

	gsub("&", "&amp;", v); gsub("<", "&lt;", v); gsub(">", "&gt;", v);
	printf '<s:is><s:t>a%s</s:t></s:is>', v;
}
FIN