1. No need to make it a friend
  2. No need for the ABI compatibility workaround. Now this is in a library and not interpreted.

it can become a plain internal helper.

to support the PCRE dialect.
This is done because TRegexp is insufficient for common task such as
expressing an OR.
The choice is documented and a test is added.

therewith removing the need to include TInterpreter.h.

in order not to include TROOT.h in RInterface.hxx

transfer routines to InterfaceUtils and include the headers in
the cxx file. The objective is to reduce parsing time of the
RInterface.hxx header.

implemented in the ROOTDataFrame library.

* Improve documentation of RooAddition.

* Improve formatting of docs for RooMCStudy and RooAbsRealLValue.

* Improve documentation for RooMCStudy and RooAddPdf.

* Improve docs for several Roo classes: RooAbsReal, RooAbsPdf, RooAbsRealLValue, RooExtendPdf.

* Minor improvement of docs in RooAbsPdf, RooExtendPdf, RooRealIntegral

[TFormula] Allow autoparsing to hit before Declare() (ROOT-9840)

Cppyy supports C++11.

Revert PR3075: it causes
CMakeFiles/ROOTDataFrame.dir/src/RSqliteDS.cxx.o: In function `(anonymous namespace)::VfsRdOnlyRead(sqlite3_file*, void*, int, long long)':
RSqliteDS.cxx:(.text+0x237): undefined reference to `Davix::DavPosix::pread(Davix_fd*, void*, unsigned long, long, Davix::DavixError**)'

and many more.

This reverts commit 84108b50.

This reverts commit d6e02859.

This reverts commit f9201586.

It breaks the build, as doc generation for these tools imports PyROOT before it has been built.

When Davix is builtin, libdavix is static and the symbols get copied
both into RDAVIX and ROOTDataFrame, and clash at runtime because there
are multiple copies of the same symbols. To resolve this problem, we
link ROOTDataFrame to RDAVIX only, but for that we have to propagate the
include directory by using PUBLIC linking explicitly. Also, since the
header for SQLite is not needed during dictionary generation, we can
remove it from the DICTIONARY_OPTIONS of ROOTDataFrame as well.