Document this variable in state-based template entities (#22211)

Co-authored-by: Franck Nijhof <git@frenck.dev>

source/_integrations/alarm_control_panel.template.markdown

@@ -111,6 +111,10 @@ panels:
           default: number
 {% endconfiguration %}
 
+### Template variables
+
+State-based template entities have the special template variable `this` available in their templates. The `this` variable aids [self-referencing](/integrations/template#self-referencing) of an entity's state and attribute in templates.
+
 ## Considerations
 
 If you are using the state of an integration that takes extra time to load, the Template Alarm Control Panel may get an `unknown` state during startup. This results in error messages in your log file until that integration has completed loading. If you use `is_state()` function in your template, you can avoid this situation.

source/_integrations/cover.template.markdown

@@ -114,6 +114,10 @@ cover:
         type: template
 {% endconfiguration %}
 
+### Template variables
+
+State-based template entities have the special template variable `this` available in their templates. The `this` variable aids [self-referencing](/integrations/template#self-referencing) of an entity's state and attribute in templates.
+
 ## Considerations
 
 If you are using the state of a platform that takes extra time to load, the

source/_integrations/fan.template.markdown

@@ -134,6 +134,10 @@ fan:
         default: 100
 {% endconfiguration %}
 
+### Template variables
+
+State-based template entities have the special template variable `this` available in their templates. The `this` variable aids [self-referencing](/integrations/template#self-referencing) of an entity's state and attribute in templates.
+
 ## Converting from speeds to percentage
 
 When converting a fan with 3 speeds from the old fan entity model, the following percentages can be used:

source/_integrations/light.template.markdown

@@ -179,6 +179,10 @@ light:
         type: action
 {% endconfiguration %}
 
+### Template variables
+
+State-based template entities have the special template variable `this` available in their templates. The `this` variable aids [self-referencing](/integrations/template#self-referencing) of an entity's state and attribute in templates.
+
 ## Considerations
 
 If you are using the state of a platform that takes extra time to load, the

source/_integrations/lock.template.markdown

@@ -75,6 +75,10 @@ lock:
     default: false
 {% endconfiguration %}
 
+### Template variables
+
+State-based template entities have the special template variable `this` available in their templates. The `this` variable aids [self-referencing](/integrations/template#self-referencing) of an entity's state and attribute in templates.
+
 ## Considerations
 
 If you are using the state of a platform that takes extra time to load, the Template Lock may get an `unknown` state during startup. This results in error messages in your log file until that platform has completed loading. If you use `is_state()` function in your template, you can avoid this situation. For example, you would replace {% raw %}`{{ state('switch.source') == 'on') }}`{% endraw %} with this equivalent that returns `true`/`false` and never gives an unknown result: {% raw %}`{{ is_state('switch.source', 'on') }}`{% endraw %}

source/_integrations/switch.template.markdown

@@ -82,6 +82,10 @@ switch:
         type: template
 {% endconfiguration %}
 
+### Template variables
+
+State-based template entities have the special template variable `this` available in their templates. The `this` variable aids [self-referencing](/integrations/template#self-referencing) of an entity's state and attribute in templates.
+
 ## Considerations
 
 If you are using the state of a platform that takes extra time to load, the Template Switch may get an `unknown` state during startup. This results in error messages in your log file until that platform has completed loading. If you use `is_state()` function in your template, you can avoid this situation. For example, you would replace {% raw %}`{{ states.switch.source.state == 'on') }}`{% endraw %} with this equivalent that returns `true`/`false` and never gives an unknown result: {% raw %}`{{ is_state('switch.source', 'on') }}`{% endraw %}

source/_integrations/template.markdown

@@ -68,6 +68,10 @@ template:
 
 {% endraw %}
 
+### Template variables
+
+State-based template entities have the special template variable `this` available in their templates. The `this` variable aids [self-referencing](#self-referencing) of an entity's state and attribute in templates.
+
 ## Trigger-based template binary sensors, buttons, numbers, selects and sensors
 
 If you want more control over when an entity updates, you can define a trigger. Triggers follow the same format and work exactly the same as [triggers in automations][trigger-doc]. This feature is a great way to create entities based on webhook data ([example](#storing-webhook-information)), or update entities based on a schedule.
@@ -564,6 +568,24 @@ template:
 
 {% endraw %}
 
+### Self referencing
+
+This example demonstrates how the `this` variable can be used in templates for self-referencing.
+
+{% raw %}
+
+```yaml
+template:
+  - sensor:
+      - name: test
+        state: "{{ this.attributes.test }}"
+        # not: "{{ state_attr('sensor.test', 'test' }}"
+        attributes:
+          test: "{{ now() }}"
+```
+
+{% endraw %}
+
 ## Legacy binary sensor configuration format
 
 _This format still works but is no longer recommended. [Use modern configuration](#configuration-variables)._

source/_integrations/vacuum.template.markdown

@@ -103,6 +103,10 @@ vacuum:
         type: [string, list]
 {% endconfiguration %}
 
+### Template variables
+
+State-based template entities have the special template variable `this` available in their templates. The `this` variable aids [self-referencing](/integrations/template#self-referencing) of an entity's state and attribute in templates.
+
 ## Examples
 
 ### Control vacuum with Harmony Hub

source/_integrations/weather.template.markdown

@@ -87,3 +87,7 @@ forecast_template:
   required: false
   type: template
 {% endconfiguration %}
+
+### Template variables
+
+State-based template entities have the special template variable `this` available in their templates. The `this` variable aids [self-referencing](/integrations/template#self-referencing) of an entity's state and attribute in templates.