Doc: Extend the documentation about qmake scopes

Fixes: QTBUG-18025
Change-Id: I2b587266cde2002d965dc824a869be255cf3522e
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

qmake/doc/snippets/qmake/scopes.pro

@@ -40,3 +40,21 @@ win32|macx {
     HEADERS += debugging.h
 }
 #! [4]
+
+#! [5]
+if(win32|macos):CONFIG(debug, debug|release) {
+    # Do something on Windows and macOS,
+    # but only for the debug configuration.
+}
+win32|if(macos:CONFIG(debug, debug|release)) {
+    # Do something on Windows (regardless of debug or release)
+    # and on macOS (only for debug).
+}
+#! [5]
+
+#! [6]
+win32-* {
+    # Matches every mkspec starting with "win32-"
+    SOURCES += win32_specific.cpp
+}
+#! [6]

qmake/doc/src/qmake-manual.qdoc

@@ -4418,6 +4418,20 @@
 
     \snippet qmake/scopes.pro 4
 
+    If you need to mix both operators, you can use the \c if function to specify
+    operator precedence.
+
+    \snippet qmake/scopes.pro 5
+
+    The condition accepts the wildcard character to match a family of \c{CONFIG}
+    values or mkspec names.
+
+    \snippet qmake/scopes.pro 6
+
+    \note Historically, checking the mkspec name with wildcards like above was
+    qmake's way to check for the platform. Nowadays, we recommend to use values
+    that are defined by the mkspec in the \c QMAKE_PLATFORM variable.
+
     You can also provide alternative declarations to those within a scope by
     using an \c else scope. Each \c else scope is processed if the conditions
     for the preceding scopes are false.