<para>If <literal>replace-irreversibly</literal> is specified,
operate like <literal>replace</literal>, but also mark the new
jobs as irreversible. This prevents future conflicting
- transactions from replacing these jobs. The jobs can still be
- cancelled using the <command>cancel</command> command.</para>
+ transactions from replacing these jobs (or even being enqueued
+ while the irreversible jobs are still pending). Irreversible
+ jobs can still be cancelled using the <command>cancel</command>
+ command.</para>
<para><literal>isolate</literal> is only valid for start
operations and causes all other units to be stopped when the