Add cache.md.

Author: DavidLambauer

cache.md

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+# Cache.xml Reference Documentation
+
+## Introduction
+
+The cache.xml file is an essential configuration file in Magento 2 that controls the caching behavior of your
+application. By properly configuring this file, you can optimize the caching process, improve performance, and enhance
+the overall user experience of your Magento 2 website.
+
+In this reference documentation, we will explore the structure and key elements of the cache.xml file. We will provide
+you with concrete examples and code snippets to help you understand and leverage the power of cache.xml in your Magento
+2 projects.
+
+## Understanding the Structure
+
+The cache.xml file is located in the `app/etc/` directory of your Magento 2 installation. It follows a hierarchical
+structure with a root `<config>` element, which contains multiple `<type>` elements representing different cache types.
+
+```xml
+
+<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+        xsi:noNamespaceSchemaLocation="urn:magento:framework:Cache/etc/cache.xsd">
+    <type name="cache_type1"/>
+    <type name="cache_type2"/>
+    ...
+</config>
+```
+
+Each `<type>` element represents a cache type that can be enabled or disabled individually. Magento 2 provides several
+predefined cache types, such as `config`, `layout`, `block_html`, and `full_page`, among others. Additionally, you can
+create custom cache types to suit your specific needs.
+
+## Configuring Cache Types
+
+To optimize caching for your Magento 2 application, you can configure each cache type by adding child elements within
+the corresponding `<type>` element. These child elements define various properties and behaviors for each cache type.
+
+### Example: Configuring the `config` Cache Type
+
+```xml
+
+<type name="config">
+    <backend_model>Magento\Framework\Cache\Backend\File</backend_model>
+    <backend_model>Magento\Framework\App\Cache\StateInterface</backend_model>
+    <config_model>Magento\Framework\App\Cache\Config</config_model>
+    <cache_dir>cache_dir/config</cache_dir>
+    <description>Configuration files cache</description>
+</type>
+```
+
+In the example above, we configure the `config` cache type. Let's understand the purpose of each child element:
+
+- `<backend_model>`: Specifies the backend model responsible for storing and retrieving cached data. In this case,
+  both `Magento\Framework\Cache\Backend\File` and `Magento\Framework\App\Cache\StateInterface` are used.
+- `<config_model>`: Defines the configuration model responsible for managing the cache type. In this
+  example, `Magento\Framework\App\Cache\Config` is used.
+- `<cache_dir>`: Specifies the directory where the cached data will be stored. The value `cache_dir/config` sets the
+  cache directory for the `config` cache type.
+- `<description>`: Provides a brief description of the cache type, which can be helpful for documentation or debugging
+  purposes.
+
+You can configure other cache types in a similar manner, adjusting the specific elements and values according to your
+requirements.
+
+## Enabling and Disabling Cache Types
+
+By default, all cache types are enabled in Magento 2. However, you may choose to disable specific cache types that are
+not necessary for your particular application. Disabling cache types can help reduce the amount of data stored in the
+cache and improve performance.
+
+To enable or disable a cache type, you can modify the `<type>` element in the cache.xml file. Set the `enabled`
+attribute to either `true` or `false` to enable or disable the cache type, respectively.
+
+### Example: Disabling the `block_html` Cache Type
+
+```xml
+
+<type name="block_html" enabled="false"/>
+```
+
+In the example above, the `block_html` cache type is disabled by setting the `enabled` attribute to `false`. This can be
+useful during development or debugging stages, where you frequently modify layout or block templates.
+
+Remember to clear the cache after enabling or disabling cache types to ensure the changes take effect.
+
+## Conclusion
+
+The cache.xml file is a pivotal configuration file in Magento 2 that allows you to control the caching behavior of your
+application. By understanding its structure and utilizing the available elements, you can optimize caching, improve
+performance, and deliver a seamless user experience.
+
+In this reference documentation, we explored the structure of cache.xml, learned how to configure cache types, and
+discovered how to enable or disable them. We provided you with concrete examples and code snippets to help you apply
+these concepts in your Magento 2 projects.
+
+Now armed with this knowledge, you can harness the power of cache.xml to unleash the full potential of caching in your
+Magento 2 applications. Happy coding!