tier 1 general confusion

hi good people. i know tier 1 general is closed to new applicants switching from a lot of categories but i came across the categories below from the 'eligibility' page:
1.highly skilled migrant
2.writer, composer or artist
3.self-employed lawyer
4.Tier 1 (General)
5.Highly Skilled Migrant Programme (HSMP), if you are eligible to switch into 6.Tier 1 (General).

my question is what is the difference between 'HIGHLY SKILLED MIGRANT' (1 above) and HIGHLY SKILLED MIGRANT PROGRAMME (HSMP).......(5 above) as used here? thank you.

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the actual rules are clearer. See para 245CA(f)

thank you