When matching over a QString we store a (shallow) copy of it. That has always been an implementation detail and people should've never relied on it, but Hyrum's law, we don't want to actually exploit this by NOT taking the copy. Converesely, matching over QStringView already requires that the string data is kept alive as long as QRE(Match) objects are alive. Add a doc note to give us the freedom to do the change in Qt 7. [ChangeLog][QtCore][QRegularExpression] QRegularExpression takes a shallow copy of a QString subject when matching over it. This means that users can destroy or modify the string data while still having match results over it. This behavior is deprecated; in a future version of Qt, QRegularExpression will no longer take a copy. Note that behavior has always been undocumented and users were never supposed to modify a subject string while match objects were alive on it. In practice, it's very unlikely that your code is relying on the existing behavior. Change-Id: Ibc5f900c09a007139fb12fc4d7f11e4a8f31bf38 Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>