MUI_PAGE_CUSTOMFUNCTION_SHOW documentation

The documentation about the

MUI_PAGE_CUSTOMFUNCTION_PRE

MUI_PAGE_CUSTOMFUNCTION_SHOW

MUI_PAGE_CUSTOMFUNCTION_LEAVE

in ./Contrib/Modern%20UI/Readme.html#customFunctions

is not clear to me. Are the callbacks called for every page or is there a way to register them for specific pages?

Like all page settings, it applies to one page. You should add the setting before a page macro.

E.g.
!define MUI_PAGE_CUSTOMFUNCTION_PRE "myWelcome_Pre"
!insertmacro MUI_PAGE_WELCOME

-Stu