Meaning of PageStyle as a class parameter

[ehud.behar at protonmail.com]

I am building my layout file and I want to better understand the effect of

PageStyle empty|myheadings|...

Inserting this line into my layout file does not make any apparent effect.

Moreover, I looked at the content of `memoir.layout` and I see that there are multiple page styles for this doc class:

`PageStyle   empty|plain|headings|myheadings|ruled|Ruled|companion`

After loading this layout file, when I go to Document Settings->Page Layout, I see in the drop-down the only the four regular ones: Default,empty,plain,headings and fancy.

I expected the drop down list to be updated according to the arguments pass to `PageStyle`.

Then what is the meaning of this class parameter?