Short answer
The subclass 187 RSMS visa is a permanent employer-sponsored visa pathway connected to regional sponsored employment. This source focuses on the Temporary Residence Transition stream.
Subclass 187 sits within the Permanent Employer Sponsored Entry program. This draft covers the RSMS visa application process for applicants nominated in the Temporary Residence Transition stream.
The pathway depends on the employer nomination, the nominated position and the applicant meeting the relevant visa criteria. It is not a general skilled visa that an applicant can pursue without the employer-sponsored nomination pathway.