turn username into a profile link

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XThreads itself supports multiple values (comma separated for textbox and new line for textarea).
The problem is validating whether the username(s) entered by the user is a valid username or not, including whether they are duplicate or not (for example: User 1, User 2, User 1).
If you store the username inside the custom field, it won't be updated automatically if the user decides to change the usernames (character names).
So, you need an additional plugin for that.
The alternative way is store the uid(s) rather than the username(s). But still, you still need the validation and an additional plugin to load the usernames based on the uid to turn them into a profile link.