Lesson 7.2: extension.xml, ezinfo.php and a license #

An extension tells the system who it is in two small files, ezinfo.php and extension.xml. The About page, the Extensions page and the upgrade checks read them, and anyone who finds the extension on a server learns from them which release it is and under which license it may be used. In this lesson learners give mysite_hello its identity and a license.

At a glance #

Learning objectives #

After this lesson, learners can:

• write ezinfo.php with a static info() returning Name, Version, Copyright, License and Info_url;
• write extension.xml with a <metadata> block that agrees with ezinfo.php;
• add a LICENSE file whose name matches the license line;
• check both files with php -l and xmllint --noout and on the About page (/ezinfo/about);
• explain why version fields are raised before a release tag, never after.

Trainer's notes #

How to present it #

Sources: ezinfo.php: what the About page reads, extension.xml: the packaged description and Specification: extension metadata.

1. ezinfo.php (4 minutes). The class is the folder name followed by Info, info() is static, every key is a quoted string. Show extension/cjw_themes_jumper/ezinfo.php if installed.
2. extension.xml (3 minutes). <software><metadata> with <name>, <version>, <copyright>, <license>, <info_url>. The About page reads extension.xml first when it has <metadata>, so both files must agree.
3. Values never to write (2 minutes). //autogentag// or dev-master as a version; a license that differs from the LICENSE file; a website that is not yours.
4. The license (3 minutes). Code that builds on the kernel is usually under the GNU GPL, version 2 or later; the license line reads "GNU General Public License v2.0 (or any later version)". Choosing a license is the author's decision; Licensing choices explains the options.
5. Versions and tags (3 minutes). A release raises the version in both files in the commit the tag points at. A pushed tag is permanent; a mistake is fixed by the next version, never by moving a tag.

Common questions #

Does a private extension need a license? A license file says how others may use the code; for an extension that never leaves your company, the copyright line is still worth keeping correct.

What else carries a version? A version in composer.json if you keep one, and a version header in a share/filelist.md5 if the extension has one; they move together.

Which version number for a first release? Your choice; the designers' distribution pages explain the convention that only the last position counts on (1.0.9 is followed by 1.0.10).

Pitfalls #

• A non-static info() or unquoted keys. The About page shows dashes.
• Different values in the two files. The About page shows the extension.xml values, which may be the stale ones.
• Copying a license line from another extension. It must match your own LICENSE file.

Hands-on exercise #

On the development installation, in extension/mysite_hello.

1. Create ezinfo.php:

   <?php
   class mysite_helloInfo
   {
       public static function info()
       {
           return array(
               'Name'      => "Mysite Hello",
               'Version'   => "0.1.0",
               'Copyright' => "Copyright (C) 2026 <your name>",
               'License'   => "GNU General Public License v2.0 (or any later version)",
               'Info_url'  => "https://example.invalid/mysite_hello",
           );
       }
   }

2. Create extension.xml with the same values:

   <?xml version="1.0" encoding="utf-8" ?>
   <software>
       <metadata>
           <name>Mysite Hello</name>
           <version>0.1.0</version>
           <copyright>Copyright (C) 2026 your name</copyright>
           <license>GNU General Public License v2.0 (or any later version)</license>
           <info_url>https://example.invalid/mysite_hello</info_url>
       </metadata>
   </software>

3. Add a LICENSE file with the full text of the GNU GPL version 2, for example a copy of extension/ezformtoken/LICENSE, which ships in the kernel repository.

4. Check: php -l extension/mysite_hello/ezinfo.php and xmllint --noout extension/mysite_hello/extension.xml.

5. Open the About page, /ezinfo/about in the administration (heading "Exponential information"), and find the row of mysite_hello under Extensions.

6. Change the version in extension.xml only to 0.1.1, reload the About page, and see which value wins. Put both files back to the same version.

7. Commit the three files with the message Added: Extension metadata and license.

Expected result #

• Step 4: No syntax errors detected and no output from xmllint.
• Step 5: a row with the name, version, license and website.
• Step 6: the About page shows 0.1.1, the extension.xml value.
• The trainer checks one learner's About page row.

Quiz #

1. What is the class name in ezinfo.php of the extension mysite_hello?
2. Which file does the About page read first when both have values? A. ezinfo.php B. extension.xml C. composer.json D. LICENSE
3. Name two values that must never be written as a version.
4. When is the version raised for a release: before or after the tag?
5. Which command checks that extension.xml is well formed?

Further reading #

• ezinfo.php and extension.xml.
• Keeping every version field in sync.
• The LICENSE file and Licensing choices.
• A pushed tag is permanent.

Related pages #

• Module 7: Extensions
• Developers: course overview
• Trainers: start here
• Free documentation: this page is free to copy, translate and improve under the GNU FDL 1.3.