Add requirements to header files and specification version macro

source/elements/oneDPL/source/common.rst

@@ -2,14 +2,51 @@
 ..
 .. SPDX-License-Identifier: CC-BY-4.0
 
+General Information
+-------------------
+
+This section describes the most general functionality of |dpl_full_name| (oneDPL)
+such as namespaces, versioning, etc.
+
 Namespaces
-----------
+++++++++++
 
 oneDPL uses ``namespace oneapi::dpl`` and a shorter variant ``namespace dpl`` for all
 functionality including parallel algorithms, oneDPL execution policies, etc.
 For the subset of the standard C++ library for kernels, the standard class
 and function names are also aliased in ``namespace oneapi::dpl``.
 
 oneDPL uses nested namespaces for the functionality aligned with the C++ standard.
-The names of those namespaces are the same as in ``namespace std``. For example,
-oneDPL execution policies are provided in ``namespace oneapi::dpl::execution``.
+The names of those namespaces are the same as for their analogues in ``namespace std``.
+[*Example*: oneDPL execution policies are provided in ``namespace oneapi::dpl::execution``.  -- *end example*]
+
+Header Files
+++++++++++++
+
+The oneDPL header files are provided under the ``oneapi/dpl/`` include path,
+which must explicitly precede oneDPL header file names in ``#include`` directives.
+
+Following the naming convention for the C++ standard library header files,
+the oneDPL header files have no extension suffix in their names.
+
+A oneDPL header file automatically includes the C++ standard library header file
+which name matches that of the oneDPL header file without the include path prefix.
+[*Example*: ``#include <oneapi/dpl/version>`` automatically includes ``<version>`` 
+if that is available. -- *end example*]
+
+Version Information
++++++++++++++++++++
+
+A oneDPL implementation must define a preprocessor macro representing the version
+of the oneDPL specification that the implementation is compliant with.
+
+.. code:: cpp
+
+  // Defined in <oneapi/dpl/version>
+
+  #define ONEDPL_SPEC_VERSION /*implementation-defined*/
+
+The ``ONEDPL_SPEC_VERSION`` macro must be defined to the decimal literal which value equals to
+*major-spec-version* * 100 + *minor-spec-version*, where *major-spec-version* and *minor-spec-version*
+are the major and the minor versions of the latest fully supported specification.
+[*Example*: ``#define ONEDPL_SPEC_VERSION 104`` for the oneDPL specification 1.4.  -- *end example*]