The issue

You can not set the text-align CSS property of a Paragraph block to justify. If you add it manually via Edit as HTML, the block will become invalid. Justified text alignment should be allowed, even if it is not exposed through the UI.

How to reproduce

1. Insert a Paragraph block.
2. Click the ellipsis (More Options) and choose Edit as HTML.
3. Add the following to the <p> tag: style="text-align:justify".
4. Try unfocusing the block.
5. Notice that the block becomes invalid.

Related issues and PRs

• Classic + Custom HTML blocks: Convert to Blocks removes valid inline formatting #6102
• Block Validation, Deprecation and Migration Experience #7604
• Block validation triggers when reverting a class change #8131