What is first-to-file rule in trademark law?

The Trademark Law adopts a first-to-file rule for obtaining trademark rights. The first applicant to file an application for registration of a mark will pre-empt all other later applications for the same mark in the same class. If two or more applications are filed for the same mark in the same class on the same day, the trademark used first shall be accepted.

Where an application to register a mark has been rejected due to its identity or similarity to a previously registered mark, evidence of prior use will not be helpful for the purpose of challenging the registration, unless the mark is proved to be "well-known"under the law.