Possible arguments for dirichlet

NGSolve
1

For the one line of code below, what are all possible options and their meanings for the arguments I can put after dirichlet? Thanks.
V = H1(mesh, order=order, dirichlet=“.*”)

2

The documentation you get from

help(H1)

tells:

 |  dirichlet: regexpr
 |    Regular expression string defining the dirichlet boundary.
 |    More than one boundary can be combined by the | operator,
 |    i.e.: dirichlet = 'top|right'

However, it does not tell that you can also use a Region objection, like

fes = H1(mesh, dirichlet=mesh.Boundaries("left"))

more on regions you find in https://docu.ngsolve.org/latest/i-tutorials/unit-1.5-subdomains/subdomains.html

Joachim