Documentation for Jinja import (#26436)

source/_docs/configuration/templating.markdown

@@ -65,6 +65,39 @@ extensions:
 
 * [Loop Controls](https://jinja.palletsprojects.com/en/3.0.x/extensions/#loop-controls) (`break` and `continue`)
 
+### Reusing Templates
+
+You can write reusable Jinja templates by adding them to a `custom_jinja` folder under your
+configuration directory. All template files must have the `.jinja` extension and be less than 5MiB.
+Templates in this folder will be loaded at startup. To reload the templates without
+restarting Home Assistant, invoke the `homeassistant.reload_custom_jinja` service.
+
+Once the templates are loaded, Jinja [includes](https://jinja.palletsprojects.com/en/3.0.x/templates/#include) and [imports](https://jinja.palletsprojects.com/en/3.0.x/templates/#import) will work
+using `config/custom_jinja` as the base directory.
+
+For example, you might define a macro in a template in `config/custom_jinja/formatter.jinja`:
+
+{% raw %}
+
+```text
+{% macro format_entity(entity_id) %}
+{{ state_attr(entity_id, 'friendly_name') }} - {{ states(entity_id) }}
+{% endmacro %}
+```
+
+{% endraw %}
+
+In your automations, you could then reuse this macro by importing it:
+
+{% raw %}
+
+```text
+{% from 'formatter.jinja' import format_entity %}
+{{ format_entity('sensor.temperature') }}
+```
+
+{% endraw %}
+
 ## Home Assistant template extensions
 
 Extensions allow templates to access all of the Home Assistant specific states and adds other convenience functions and filters.

source/_integrations/homeassistant.markdown

@@ -29,11 +29,16 @@ Reload all YAML configuration that can be reloaded without restarting Home Assis
 
 It calls the `reload` service on all domains that have it available. Additionally,
 it reloads the core configuration (equivalent to calling
-`homeassistant.reload_core_config`) and themes (`frontend.reload_themes`).
+`homeassistant.reload_core_config`), themes (`frontend.reload_themes`), and custom Jinja (`homeassistant.reload_custom_jinja`).
 
 Prior to reloading, a basic configuration check is performed. If that fails, the reload
 will not be performed and will raise an error.
 
+### Service `homeassistant.reload_custom_jinja`
+
+Reload all Jinja templates in the `config/custom_jinja` directory. Changes to these templates
+will take effect the next time an importing template is rendered.
+
 ### Service `homeassistant.reload_config_entry`
 
 Reloads an integration config entry.