Forumlar / Cotonti / Support / Can't save [rel="xxx"] property in hyperlinks

I tried to add rel="gallery" in hyperlinks.

For example:

<a rel="gallery" href="xxx">demo</a>

But [rel="gallery"] always disappeared after article was published.

It displayed like this:

<a href="xxx">demo</a>

Could you please help me to solve this problem?

Added 1 hours later:

It seems like a "html purifier" problem~