it allows you to put expiration on your code comments.
a comment can expire by e.g. a github, jira or youtrack issue-url. expiration dates and composer version constraints also work.
As of 0.1.16 #phpstan#todoBy learnt to expire comments based on issue ticket references. This means when a ticket is 'resolved' leftover todos will error.
ATM only JIRA is supported - thanks to @EMasiakowski