> In this release the Material Property Library is significantly enriched with new constitutive relations and gets wide use in the processes.
>
> Other significant changes are:
## Features
### Process' changes
- Richards mechanics process now correctly computes porosity changes in presence of swelling. [#2825](https://github.com/ufz/ogs/pull/2825)
- HydroMechanics process has now the option to use mass lumping. [#2826](https://github.com/ufz/ogs/pull/2826)
- HydroMechanics process now uses permeability in tensor form with corresponding output. [#2848](https://github.com/ufz/ogs/pull/2848)
- Reactive transport process has a mesh tag for restricting the place where chemical reactions take place within a specified subdomain. [#2851](https://github.com/ufz/ogs/pull/2851)
#### Numerics
- Pass `x_dot` to processes' assemble functions. Used by rate-dependent material models. [#2795](https://github.com/ufz/ogs/pull/2795)
- triangular elements with 7 integration points (order 4). [#2798](https://github.com/ufz/ogs/pull/2798)
#### Input and output
- Output of surface fluxes (for 2D and 3D bulk domains) for balance computations is now available for LiquidFlow process. [#2760](https://github.com/ufz/ogs/pull/2760)
- Compute and output element-average porosity in RichardsMechanics process. [#2803](https://github.com/ufz/ogs/pull/2803)
- Output of fixed time when using IterationBasedTimeStepping is now available. [#2831](https://github.com/ufz/ogs/pull/2831)
### Material models
- Enable orthotropy in MFront solid material model interface. [#2774](https://github.com/ufz/ogs/pull/2774)
- Enable shared medium definition for multiple materials. [#2786](https://github.com/ufz/ogs/pull/2786)
- Implement van Genuchten saturation and relative permeability models in MPL. [#2788](https://github.com/ufz/ogs/pull/2788)
- Convert processes to use MPL for the fluid and porous media models:
- Pass time increment dt to the material models. [#2801](https://github.com/ufz/ogs/pull/2801)
- Add initialValue(x, t) for material properties. [#2804](https://github.com/ufz/ogs/pull/2804)
- Implement mass balance porosity, used in RichardsMechanics. [#2804](https://github.com/ufz/ogs/pull/2804), [#2829](https://github.com/ufz/ogs/pull/2829)
- Orthotropic permeability power law, used in RichardsMechanics. [#2813](https://github.com/ufz/ogs/pull/2813)
- Implement saturation dependent swelling, used in RichardsMechanics. [#2819](https://github.com/ufz/ogs/pull/2819), [#2832](https://github.com/ufz/ogs/pull/2832)
- Bishop's effective stress models; power law and saturation cutoff, used in RichardsMechanics. [#2823](https://github.com/ufz/ogs/pull/2823)
### File I/O
### Testing and documentation
- A new test verifies the correct conversion from *PropertyType* enum to string and back. [#2770](https://github.com/ufz/ogs/pull/2770)
### New tools
- ExtractEntireSurface: The tool extracts either lines in case of a 2D bulk mesh as input or quads/triangles in case of a 3D bulk mesh as input. [#2764](https://github.com/ufz/ogs/pull/2764)
## Infrastructure
- Added a Code of Conduct. [#2834](https://github.com/ufz/ogs/pull/2834)
### CMake options changes
- Added version requirements file in json-format to have a single source used by CMake and the web site generator. [#2783](https://github.com/ufz/ogs/pull/2783)
### Version info
- See [versions.json](https://github.com/ufz/ogs/blob/6.3.0/web/data/versions.json)