[Vuejs]-How to force Tagify to only accept tags made of lowercase and underscores?

I haven’t quite found the perfect answer, but this seems to work okay:

var newSetTags = document.getElementById("new-set-tags");
var tagify = new Tagify(newSetTags, { pattern: /^[a-z][a-z_]+$/gm });

The pattern parameter validates the tags.