When viewing code snippets in Trello you may notice some of the text is highlighted, these texts represent bidirectional characters. Bidirectional characters are used to specify the order that characters should be rendered, for example, to support right-to-left languages (e.g. Arabic, Urdu, etc.). However, these characters could also be used maliciously to make a code snippet appear to do one thing, but actually do another. For this reason, we highlight bidirectional characters so you can identify them in code snippets in Trello.
You can find more information about this here: https://confluence.atlassian.com/display/SECURITY/CVE-2021-42574+-+Unrendered+unicode+bidirectional+override+characters+in+Cloud+sites
Bidirectional character warnings on web
You'll be able to see a tooltip that states:
Bidirectional characters change the order that text is rendered. This could be used to obscure malicious code.