Escape special XML characters, e.g.
<a1>→<a1>. More information: https://xmlstar.sourceforge.net/doc/UG/xmlstarlet-ug.html#idm47077139540960.
xml {{[esc|escape]}} "{{<a1>}}"
stdin:echo "{{<a1>}}" | xml {{[esc|escape]}}
xml {{[esc|escape]}} --help