Try to type space between tags

If it's a single text box then I have found that typing the tag name followed by seni-colon then space works: _tag; tag2; tag3; ...tagN_

Neither spaces nor semicolons are working for me. If I put in too many terms, I get a "request invalid" error box. Fortunately, I don't have that many pcblib parts - I can always scroll down.

Do a Shift+F search for your PCB lib then select and right-click Modify. You should have access to the Tags box then. Does that help?

Yes, that's the UI I'm using:  I can submit the dialog (no error screen today), but when I search again using one of the tags, I don't get any results: 

@alan.green At now, EasyEDA doesn't support search tag directly, please hover the cursor to the "personal" class. 

I see, thank you!