What is accountId format. Is there any public definition?

We use pdcleaner (https://developer.atlassian.com/cloud/jira/platform/rest/v3/api-group-jql/#api-rest-api-3-jql-pdcleaner-post) for changing userKey from input JQLs in our application. Apart from cleaning personal data this endpoint changes JQL syntactics. I would like to distinguish situation in which pdcleaner removed personal data from situation when only syntactics was changed. Therefore knowing AccountID regex would greatly help

According to https://developer.atlassian.com/cloud/jira/platform/user-privacy-developer-guide/#reporting-user-personal-data-for-your-apps

An accountId uniquely identifies a user across all Atlassian products. It is 1-128 characters long and may contain alphanumeric characters as well as - and : characters

You cannot assume anything else about their format as they have changed over time (e.g. some are only alphanumeric and some contain - or :).

Thank you @raimonds.simanovskis !