Requested feature overview description.
A mechanism to suggest tags based on what you are writing in any text field of the site where tags are expected.

It would be the same as the Danbooru system (NSFW): writing the beginning of a tag on a text field will generate suggestions besides it with tags that either begins with the string you wrote, or a alias that matches that.

It should avoid to suggest empty tags (no posts marked with it).

Why would it be useful?

It could be useful to:

• Make tagging faster;
• Help making the user be sure if a tag exists or not without needing to double check in another page;
• Since it matches aliases, it could show the user that the tag they are trying to add is an invalid_tag.

What part(s) of the site page(s) are affected?

Any page where the user is expected to write tags. Examples:

• The posts page;
• The upload page;
• The tags page;
• The aliases page;

... and etc.