Add tag website build text to README.md (#2113)

README.md

@@ -39,6 +39,7 @@ The file ReadMe.txt in a build bundle describes how to install the library on th
     - [Using pkg-config to compile and link your code with Exiv2](#ConsumeWithPkgConfig)
     - [Localisation](#Localisation)
     - [Building Exiv2 Documentation](#BuildDoc)
+    - [Building Exiv2 Tag Webpages](#BuildTagWebpages)
     - [Building Exiv2 Packages](#GeneratePackages)
     - [Debugging Exiv2](#Debugging)
     - [Building  Exiv2 with Clang and other build chains](#BuildWithClangAndOthers)
@@ -52,6 +53,7 @@ The file ReadMe.txt in a build bundle describes how to install the library on th
     - [License](#License)
     - [Support](#Support)
 - [Test Suite](#TestSuite)
+    - [Exiv2 Environment Variables](#EnvironmentVariables)
     - [Running tests on a UNIX-like system](#TestsOnUnix)
     - [Running tests on Visual Studio builds](#TestsOnVisualStudio)
     - [Unit Tests](#UnitTests)
@@ -398,6 +400,38 @@ To build the documentation, you must install the following products:
 |:------------ |:------------ |
 | doxygen<br/>graphviz<br/>python<br/>xsltproc<br/>md5sum  | [http://www.doxygen.org/](http://www.doxygen.org/)<br/>[http://www.graphviz.org/](http://www.graphviz.org/)<br/>[http://www.python.org/](http://www.python.org/)<br/>[http://xmlsoft.org/XSLT/](http://xmlsoft.org/XSLT/)<br/>[http://www.microbrew.org/tools/md5sha1sum/](http://www.microbrew.org/tools/md5sha1sum/) |
 
+[TOC](#TOC)
+<div id="BuildTagWebpages">
+
+## Building Exiv2 Tag Webpages
+
+Exiv2 provides many built-in metadata tags which are listed in the sub-pages of https://exiv2.org/metadata.html 
+and https://pre-release.exiv2.org/metadata.html. Those tag webpages are generated using tag information 
+extracted from the Exiv2 source code.
+
+The tag webpage build files are in the `<exiv2dir>/doc/templates` directory. If changes are made to 
+tag groups in the Exiv2 source code then the build files need to be updated. Any changes made 
+to individual tags in an existing tag group are automatically included.
+
+Building the tag webpages requires building the Exiv2 sample programs and using scripts which have additional dependancies on 
+[BASH](https://www.gnu.org/software/bash/), [make](https://manpages.org/make), [xsltproc](https://manpages.org/xsltproc) 
+and [Python3](https://www.python.org/).
+
+To build the tag webpages, first [build Exiv2 from source](#TOC) with the `-DEXIV2_BUILD_SAMPLES=ON` 
+option enabled. This is required as the [taglist](README-SAMPLES.md#taglist) sample program is used by one of the scripts.
+
+Next, set the `EXIV2_BINDIR` environment variable (see [Exiv2 environment variables](#EnvironmentVariables)).
+
+Then, change directory to `doc/templates` and run `make`.
+
+```bash
+$ cd <exiv2dir>/doc/templates
+$ make
+```
+
+After processing, the generated webpages are stored in the `<exiv2dir>/doc/templates` directory. 
+When the Exiv2 websites are updated, the generated tag webpages are reformatted before use.
+
 [TOC](#TOC)
 <div id="GeneratePackages">
 
@@ -867,9 +901,16 @@ Visual Studio Users will appreciate the python implementation as it avoids the i
 
 If you build the code in the directory `<exiv2dir>/build`, tests will run using the default values of Environment Variables.
 
+[TOC](#TOC)
+<div id="EnvironmentVariables">
+
+## Exiv2 Environment Variables
+
+Exiv2 optionally uses several different environment variables when building or testing.
+
 | Variable           | Default                    | Platforms          | Purpose |
 |:--                 |:--                         |:--                 |:--      |
-| EXIV2_BINDIR       | **\<exiv2dir\>/build/bin** | All Platforms      | Path of built binaries (exiv2.exe) |
+| EXIV2_BINDIR       | **\<exiv2dir\>/build/bin** | All Platforms      | Path of built binaries (e.g., exiv2.exe) |
 | EXIV2_PORT         | **12762**<br>**12671**<br>**12760**             | Cygwin<br>MinGW/msys2<br>Other Platforms | Test TCP/IP Port   |
 | EXIV2_HTTP         | **http://localhost**       | All Platforms      | Test http server   |
 | EXIV2_ECHO         | _**not set**_              | All Platforms      | For debugging bashTests |
@@ -1297,5 +1338,5 @@ $ sudo pkg install developer/gcc-7
 
 [TOC](#TOC)
 
-Written by Robin Mills<br>robin@clanmills.com<br>Updated: 2021-12-20
+Written by Robin Mills<br>robin@clanmills.com<br>Updated: 2022-02-22
 

doc/templates/Makefile

@@ -166,7 +166,7 @@ SCHEMA = xmp_dc \
          xmp_mwg-rs \
          xmp_mwg-kw
 
-TAGLIST = ${EXIV2HOME}/build/bin/taglist
+TAGLIST = ${EXIV2_BINDIR}/taglist
 
 # **********************************************************************
 # ======================================================================