This is really a note to Wix Knowledge Base compilers that an article could use some further information in order to be as informative as most are. I'm hoping that someone at Wix monitors this forum and might take note.
The article Velo: About Mixins seems to suggest that clicking on one of two links will provide further information. In fact, the modal dialog that arises contains nothing further. That might be corrected. That's my wish anyway.
See the two attachments.