QRegularExpression: mention raw string literal in the docs

Raw string literals (since C++11 according to [1]), make writing/reading
regex patterns easier, since one can just use e.g. "\w\d" without having
to escape those backslashes e.g. "\\w\\d"; this is especially useful with
longer/more complex regex patterns.

[1] https://en.cppreference.com/w/cpp/language/string_literal

Pick-to: 5.15 6.0
Change-Id: I119f9566d27222b915af931ee7e13e064baede61
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Reviewed-by: André Hartmann <aha_1980@gmx.de>

src/corelib/doc/snippets/code/src_corelib_text_qregularexpression.cpp

@@ -357,6 +357,8 @@ QString wildcard = QRegularExpression::wildcardToRegularExpression("*.jpeg");
 
 {
 //! [34]
+// using a raw string literal, R"(raw_characters)", to be able to use "\w"
+// without having to escape the backslash as "\\w"
 QRegularExpression re(R"(\w+)");
 QString subject("the quick fox");
 for (const QRegularExpressionMatch &match : re.globalMatch(subject)) {
@@ -364,4 +366,12 @@ for (const QRegularExpressionMatch &match : re.globalMatch(subject)) {
 }
 //! [34]
 }
+
+{
+//! [35]
+// matches two digits followed by a space and a word
+QRegularExpression re(R"(\d\d \w+)");
+//! [35]
+}
+
 }

src/corelib/text/qregularexpression.cpp

@@ -140,6 +140,14 @@ QT_BEGIN_NAMESPACE
 
     \snippet code/src_corelib_text_qregularexpression.cpp 2
 
+    Alternatively, you can use a
+    \l {https://en.cppreference.com/w/cpp/language/string_literal} {raw string literal},
+    in which case you don't need to escape backslashes in the pattern, all characters
+    between \c {R"(...)"} are considered raw characters. As you can see in the following
+    example, this simplifies writing patterns:
+
+    \snippet code/src_corelib_text_qregularexpression.cpp 35
+
     The pattern() function returns the pattern that is currently set for a
     QRegularExpression object: