Help: Clarify that <PackageName>_ROOT variable names are case-preserved

The name comes from the case-preserved first argument to
`find_package`.

Help/command/find_package.rst

@@ -370,7 +370,8 @@ enabled.
 1. .. versionadded:: 3.12
     Search paths specified in the :variable:`<PackageName>_ROOT` CMake
     variable and the :envvar:`<PackageName>_ROOT` environment variable,
-    where ``<PackageName>`` is the package to be found.
+    where ``<PackageName>`` is the package to be found
+    (the case-preserved first argument to ``find_package``).
     The package root variables are maintained as a stack so if
     called from within a find module, root paths from the parent's find
     module will also be searched after paths for the current package.

Help/envvar/PackageName_ROOT.rst

@@ -7,10 +7,10 @@
 
 Calls to :command:`find_package(<PackageName>)` will search in prefixes
 specified by the ``<PackageName>_ROOT`` environment variable, where
-``<PackageName>`` is the name given to the :command:`find_package` call
-and ``_ROOT`` is literal.  For example, ``find_package(Foo)`` will search
-prefixes specified in the ``Foo_ROOT`` environment variable (if set).
-See policy :policy:`CMP0074`.
+``<PackageName>`` is the (case-preserved) name given to the
+:command:`find_package` call and ``_ROOT`` is literal.
+For example, ``find_package(Foo)`` will search prefixes specified in the
+``Foo_ROOT`` environment variable (if set).  See policy :policy:`CMP0074`.
 
 This variable may hold a single prefix or a list of prefixes separated
 by ``:`` on UNIX or ``;`` on Windows (the same as the ``PATH`` environment

Help/variable/PackageName_ROOT.rst

@@ -5,10 +5,10 @@
 
 Calls to :command:`find_package(<PackageName>)` will search in prefixes
 specified by the ``<PackageName>_ROOT`` CMake variable, where
-``<PackageName>`` is the name given to the :command:`find_package` call
-and ``_ROOT`` is literal.  For example, ``find_package(Foo)`` will search
-prefixes specified in the ``Foo_ROOT`` CMake variable (if set).
-See policy :policy:`CMP0074`.
+``<PackageName>`` is the (case-preserved) name given to the
+:command:`find_package` call and ``_ROOT`` is literal.
+For example, ``find_package(Foo)`` will search prefixes specified in the
+``Foo_ROOT`` CMake variable (if set).  See policy :policy:`CMP0074`.
 
 This variable may hold a single prefix or a
 :ref:`semicolon-separated list <CMake Language Lists>` of multiple prefixes.