Processes the signup nonce created in signup_nonce_fields().

Adds a nonce field to the signup page.

Updates this blog’s ‘public’ setting in the global blogs table.

Sends a confirmation request email when a change of network admin email address is attempted.

Updates a blog’s post count.

Checks whether an upload is too big.

Filters the maximum upload file size allowed, in bytes.

Determines whether users can self-register, based on Network settings.

Ensures that the welcome message is not empty. Currently unused.

Deletes an associated signup entry when a user is deleted from the database.