How does powershell handle transitive / nested module imports? - powershell

Question

I always thought that doing Import-Module in my current powershell console will make the module available throughout the console.
Recently however I have learned that when doing Import-Module from within a module, things are getting complicated.
Compare:
Windows PowerShell Session State
...
Module Session State
Module session states are created whenever the module or one of its nested modules is imported into the session. When a module exports an element such as a cmdlet, function, or script, a reference to that element is added to the global session state of the session. However, when the element is run, it is executed within the session state of the module.
What I can observe, is:
# This is mod1.psm1
Import-Module -Force mod2.psm1
# end mod1.psm1
-
PS> Import-Module -Force mod1.psm1
... This will make the functions of mod2.psm1 available via mod1, when checked with Get-Module
PS> Import-Module -Force mod2.psm1
... This will make the functions of mod2 available via mod2.
I don't even fully understand the behavior here, but now comes the interesting part:
# This is mod1.psm1
function fn_load_in_mod1 {
Import-Module -Force mod2.psm1
# mod2 stuff can be used here
}
# end mod1.psm1
PS> Import-Module -Force mod1.psm1
PS> # But here, no mod2 stuff is available anymore!
I learned that to make the mod2 stuff available to my console, I need to:
# This is mod1.psm1
function fn_load_in_mod1 {
Import-Module -Force mod2.psm1 -Global
# mod2 stuff can be used here, and with the -Global switch also "outside"
}
# end mod1.psm1
But I can't make head nor tail of that session state stuff.
How am I supposed to do an Import-Module from within a module "correctly"?