rougail/docs/tutorial/disabled.rst

Define access to variable or family
==========================================

.. objectives:: Objectives

   In this section we will see what a disabled variable or family is, and why it can be interesting 
   to assign the `disabled` property to a variable or a family. We'll also learn the difference 
   between disabling and hiding families or variables. 
   Then we'll see the same thing for the `hidden` property.
   
   We will:
   
   - create a `disabled` family
   - use a new family or variable's property: the `hidden` property

Disabling and hiding are two families or variables properties. 

.. prerequisites:: Prerequisites

    - We assume that Rougail's library is :ref:`installed <installation>` on your computer.

    - It is possible to retrieve the current state of the various Rougail files manipulated in this tutorial step
      by checking out the corresponding tag of the `rougail-tutorials` git repository.
      Each tag corresponds to a stage of progress in the tutorial.
      Of course, you can also decide to copy/paste or download the tutorial files contents while following the tutorial steps.

    If you want to follow this tutorial with the help of the corresponding :tutorial:`rougail-tutorials git repository <src/branch/1.1>`, 
    this workshop page corresponds to the tags :tutorial:`v1.1_050 <src/tag/v1.1_050>` to :tutorial:`v1.1_053 <src/tag/v1.1_053>` 
    in the repository.

    ::
   
       git clone https://forge.cloud.silique.fr/stove/rougail-tutorials.git
       git switch --detach v1.1_050

.. type-along:: What a property is

Let's begin with defining what a property is:

.. glossary::

   property
   
       A property is a state (`disabled`, `mandatory`, `frozen`, `hidden`...)
       of a family, a subfamily or a variable. 
       These properties change the usual behavior of a variable or family.

Here we are going to assign the `disabled` property to the `manual` family: 

.. extinclude:: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/tag/v1.1_050/firefox/10-manual.yml
   :language: yaml
   :caption: The `manual` family has the `disabled` property set in this :file:`firefox/10-manual.yml` structure file

..
    %YAML 1.2
    ---
    version: 1.1

    manual:
      description: Manual proxy configuration
      disabled: true

      http_proxy:  # HTTP Proxy

        address:
          description: HTTP address
          type: domainname
          params:
            allow_ip: true

        port:
          description: HTTP Port
          type: port
          default: 8080

Notice that we have this `disabled: true` property assigned to the `manual` family. 
Let's launch the Rougail CLI on this structure file (whith an empty user data file):

.. raw:: html
   :class: terminal
   :url: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/tag/v1.1_050/config/01/cmd_ro.txt

.. 
    rougail -m firefox/ -u yaml -yf config/02/config.yml

The Rougail CLI outputs this: 

.. raw:: html
   :url: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/tag/v1.1_050/config/01/output_ro.html
   :class: output

We can deduce from the Rougail CLI output that the `manual` family is not taken into account by Rougail.
So what does this disabled property exactly?

.. glossary::

   disabled

       The disabled property is a property that can be assigned to a variable or a family.
       It makes the :term:`configuration` act as if the variable or family that has this property has not even been defined. 
       It simply doesn't exist (it is deactivated) for the whole configuration.

.. note:: Note that, as with any property, if a family has been disabled, all variables and sub-families that it contains are disabled.

And if we try to assign values to variables that have been disabled, here is what happens:

.. extinclude:: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/tag/v1.1_050/config/02/config.yml
   :language: yaml
   :caption: In this :file:`config/02/config.yml` user data file, we assign values to variables that have been disabled

If we launch the Rougail CLI:

.. raw:: html
   :url: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/tag/v1.1_050/config/02/cmd_ro.txt
   :class: terminal

It outputs: 

.. raw:: html
  :url: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/tag/v1.1_050/config/02/output_ro.html
  :class: output

We can see that the Rougail CLI is warning us about the variables that we are trying to assign values on which are disabled.
Because it is not logical. We are trying to assign values to variables that are not taken into account in the :term:`configuration`.

The point is that we disable them in order to expose the fact that we don't use them,
but it's not just that: if we fill them in, there might be a problem in the overall integrity of the whole :term:`configuration`.
We shall fill and use in these variables in the `Manual proxy configuration` use case context only. 
Otherwise, **we need to disable them when they are not used**.

In a practical point of view, if we fill them in, Rougail CLI will output a warning and the :term:`operator` will see it. 
He will wonder : "oh, what am I doing?", I shall fill and use in these variables only in the `Manual proxy configuration` context. 

.. type-along:: The `disabling` property is usefull in our use case

Let's look again at our use case. We have a choice between five options
in order to set the proxy mode:

.. image:: images/firefox_01.png

These five choices are: 

- No proxy
- Auto-detect proxy settings for this network
- Use system proxy settings
- Manual proxy configuration
- Automatic proxy configuration URL

Actually if the `Manual proxy configuration` is not selected, we don't need to set 
these `address` and `port` variables, there is no point in setting them in 
four out of our five use cases.

.. important:: We need to **disable** variables or families that are not used
               in a given usage context.

A disabled family
------------------

Disabling variables one by one can be replaced by disabling a whole family. 
If we don't choose the manual mode, we need to **disable** the whole `manual` family, it will disable 
all the subfamilies and the variables in it. 

Note that we've placed theses variables in the `http_proxy`
subfamily. We can then disable it or even the parent `manual` subfamily in order to 
disable the `http_proxy` family and all the variables that are placed in it, because 
the `manual` family variables shall be used only in the manual proxy use case context.

Notice the `disabled: true` parameter set in the `manual` family:

.. extinclude:: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/tag/v1.1_050/firefox/10-manual.yml
   :linenos:
   :language: yaml
   :caption: The `http_proxy` subfamily in the :file:`firefox/10-manual.yml` structure file is disabled here

.. 
    ---
    manual:
      description: Manual proxy configuration
      disabled: true

      http_proxy:
        description: HTTP Proxy

        address:
          description: HTTP address
          type: domainname
          params:
            allow_ip: true

        port:
          description: HTTP Port
          type: port
          default: 8080

A conditional disabled family
------------------------------

.. type-along:: For those who follow the tutorial with the help of the git repository

    Now you need to checkout the `v1.1_051` version::
     
          git switch --detach v1.1_051

What could be usefull here is a *dynamically* disable or enable the `manual` family. 
The idea in this section is to dynamically set the enable/disable property according to the chosen use case context.

In rougail, we can set a property's value **depending on** the value of another variable. 
**The property's value is conditioned by** another variable. 

.. extinclude:: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/tag/v1.1_051/firefox/10-manual.yml
   :linenos:
   :language: yaml
   :caption: The :file:`firefox/10-manual.yml` structure file. The `manual` family dynamically enabled or disabled

..
    %YAML 1.2
    ---
    version: 1.1

    manual:
      description: Manual proxy configuration
      disabled:
        variable: _.proxy_mode
        when_not: Manual proxy configuration

      http_proxy:  # HTTP Proxy

        address:
          description: HTTP address
          type: domainname
          params:
            allow_ip: true

        port:
          description: HTTP Port
          type: port
          default: 8080

Now the `disabled` property has some parameter defined. First, let's explaine the `variable` parameter. 
This parameter specifies the target variable. The value of this target variable 
will be used to dynamically enable or disable our `manual` family.

We can see here that the `manual` family disabled or enabled property is contitionned by the `_.proxy_mode` variable's value. 
The target variable is `_.proxy_mode`. 

.. note:: The `_.` notation means the current path of the family you're currently in.
          
          In the python quasi algorithmic notation we could say that:  
          
          .. code-block:: python
          
              _.proxy_mode == proxy_mode
              
          This is true only because in our use case `proxy_mode` is located on the root path.

Now regarding the `when_not` parameter, this means that if the target variable's value 
is `Manual proxy configuration` then the `manual` familiy **will not** be disabled 
(that is, it will be **enabled**). 

Regarding as the default value use case, the `proxy_mode`'s variable is `No proxy` by default. 
The `manual` familiy is then **disabled by default**. 

Let's launch the Rougail CLI on an empty user value file:

.. raw:: html
   :class: terminal
   :url: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/tag/v1.1_051/config/01/cmd_ro.txt

.. 
    rougail -m firefox/ -u yaml -yf config/01/config.ym

We have this output: 

.. raw:: html
   :class: output
   :url: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/tag/v1.1_051/config/01/output_ro.html

.. 
    <pre>╭──────────────────── Caption ─────────────────────╮
    │ <span style="color: #ff0000">Undocumented but modified variable</span> <span style="color: #ffd700">Default value</span> │
    ╰──────────────────────────────────────────────────╯
    Variables:
    <span style="color: #5c5cff">┗━━ </span>📓 <span style="color: #ff0000">Configure Proxy Access to the Internet</span>: <span style="color: #ffd700">No proxy</span>
    </pre>

We can see that the `manual` family and all the variables into it are not present.

.. type-along:: Dynamically enabling the `manual` family

Now we are going to choose the **manual mode**, that is the `Manual proxy configuration` 
value for the `proxy_mode` variable, and things will become slightly different.

If the manual mode for the proxy is not selected, then the `manual` family is disabled.
On the other hand, if the manual proxy's configuration mode is selected, 
then the `manual` family **is enabled**:

.. extinclude:: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/tag/v1.1_051/config/02/config.yml
   :linenos:
   :language: yaml
   :caption: The `proxy_mode`'s manual setting in the :file:`config/02/config.yaml` user datas file

..
    ---
    proxy_mode: Manual proxy configuration
    manual:
      http_proxy:
        address: http.proxy.net
        port: 3128
    use_for_https: false

Let's launch the Rougail CLI to verify this:

.. raw:: html
   :url: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/tag/v1.1_051/config/02/cmd_ro.txt
   :class: terminal 

.. 
    rougail -m firefox/ -u yaml -yf config/02/config.yml

It outputs: 

.. raw:: html
   :url: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/tag/v1.1_051/config/02/output_ro.html
   :class: output 

.. 
    <pre>╭────────────── Caption ───────────────╮
    │ Variable <span style="color: #00aa00">Modified value</span>              │
    │          (⏳ Original default value) │
    ╰──────────────────────────────────────╯
    Variables:
    <span style="color: #5c5cff">┣━━ </span>📓 proxy_mode (Configure Proxy Access to the Internet): <span style="color: #00aa00">Manual proxy </span>
    <span style="color: #5c5cff">┃   </span><span style="color: #00aa00">configuration</span> ◀ loaded from the YAML file "config/02/config.yml" (⏳ No 
    <span style="color: #5c5cff">┃   </span>proxy)
    <span style="color: #5c5cff">┗━━ </span>📂 manual (Manual proxy configuration)
    <span style="color: #5c5cff">    </span><span style="color: #5c5cff">┣━━ </span>📂 http_proxy (HTTP Proxy)
    <span style="color: #5c5cff">    </span><span style="color: #5c5cff">┃   </span><span style="color: #5c5cff">┣━━ </span>📓 address (HTTP address): <span style="color: #00aa00">http.proxy.net</span> ◀ loaded from the YAML 
    <span style="color: #5c5cff">    </span><span style="color: #5c5cff">┃   </span><span style="color: #5c5cff">┃   </span>file "config/02/config.yml"
    <span style="color: #5c5cff">    </span><span style="color: #5c5cff">┃   </span><span style="color: #5c5cff">┗━━ </span>📓 port (HTTP Port): <span style="color: #00aa00">3128</span> ◀ loaded from the YAML file 
    <span style="color: #5c5cff">    </span><span style="color: #5c5cff">┃   </span><span style="color: #5c5cff">    </span>"config/02/config.yml" (⏳ 8080)
    <span style="color: #5c5cff">    </span><span style="color: #5c5cff">┗━━ </span>📓 use_for_https (Also use this proxy for HTTPS): <span style="color: #00aa00">false</span> ◀ loaded from 
    <span style="color: #5c5cff">    </span><span style="color: #5c5cff">    </span>the YAML file "config/02/config.yml" (⏳ true)
    </pre>

.. rubric:: Explanation

Here the `disabled` property **depends on** the value of the `proxy_mode` variable. 
It is the `variable` parameter that allows you to define the name of the target variable on which the `disabled` property depends.

Please remember that this activation/deactivation of the `manual` family 
depends on the value of the `proxy_mode` variable. Here we have 
chosen the `Manual proxy configuration` value, so the `address` and `port` variables appear.

A hidden family
-------------------

.. type-along:: For those who follow the tutorial with the help of the git repository

    Now you need to checkout the `v1.1_052` version::
     
          git switch --detach v1.1_052

Let's introduce a new property here:

.. glossary:: 

   hidden
   
       A variable or family's property is hidden if its value **shall not be seen** in a given :term:`context`. 
       Anyway, these variables can be used if the context evolves. 
       
       This is the main difference between the `hidden` and the `disabled` properties:
       
       - with the `disabled` property, the variables are *deactivated*
       - with the `hidden` property, the variables are just not seen when loading the user data.

Now we can set a `hidden` property to the `https_proxy` family:

Here is our new :file:`20-manual.yml` structure file:

.. extinclude:: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/tag/v1.1_052/firefox/20-manual.yml
   :linenos:
   :language: yaml
   :caption: The :file:`firefox/20-manual.yml` structure file with the `hidden` property on the `https_proxy` family.

..
    %YAML 1.2
    ---
    version: 1.1

    manual:

      use_for_https: true  # Also use this proxy for HTTPS

      https_proxy:
        description: HTTPS Proxy
        hidden: true

        address:
          description: HTTPS address
          default:
            variable: __.http_proxy.address

        port:
          description: HTTPS Port
          default:
            variable: __.http_proxy.port
    ...

We have added two other variables for the HTTPS use only: 

.. confval:: https_proxy.address
   :type: `domainname`

   This is an address setting for the manual HTTPS configuration

.. confval:: https_proxy.port
   :type: `port`

   This is a port setting for the manual HTTPS configuration

We have now a `hidden` property assigned to the `https_proxy` family, which is 
hiding these two variables.

A conditional hidden family
----------------------------

.. type-along:: For those who follow the tutorial with the help of the git repository

    Now you need to checkout the `v1.1_053` version::
     
          git switch --detach v1.1_053

Now we will focus on configuring the HTTPS mode in case of `"Manual proxy configuration"` value has been chosen,
let's have a look at our use case again:

.. image:: images/firefox_manual_https.png

Let's have a look at the HTPPS configuration corresponding structure file:

.. extinclude:: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/commit/v1.1_053/firefox/20-manual.yml
   :linenos:
   :language: yaml 
   :caption: the :file:`firefox/20-manual.yml` structure file

.. 
    %YAML 1.2
    ---
    version: 1.1

    manual:

      use_for_https: true  # Also use this proxy for HTTPS

      https_proxy:
        description: HTTPS Proxy
        hidden:
          variable: _.use_for_https

        address:
          description: HTTPS address
          default:
            variable: __.http_proxy.address

        port:
          description: HTTPS Port
          default:
            variable: __.http_proxy.port
    ...

Let's introduce a new Rougail concept here:

.. glossary:: 

   context
   
       A :term:`configuration` is highly statefull and can change at any moment.
       Sometimes somes minor changes in the :term:`user data <user data>` may involve chain reactions 
       in the whole :term:`configuration`.
       The **context** is the state of the user data at one moment, the set of the values of the variables
       at a given moment. 
       
       This term refers in Rougail to the ability of a system to handle 
       the *statefull* state of a configuration. 
       It expresses the transition between one situation to another situation, 
       that is, the deeply **statefull** aspects of a data set.

.. type-along:: A new variable which has the `boolean` type

The best way to reproduce the `"Also use this HTTP proxy variables for HTTPS"` checkbox in the firefox interface
is to add this `use_for_https` variable in our structure file. This boolean variable can reproduce this binary choice option.

- if the use of the proxy variables for https are the same of the proxy variables for http, 
  that is, if `use_for_https` is true, the https configuration variables are hidden, that's OK. 
- if the use of the proxy variables for https **are not** the same of the proxy variables for http, 
  we would like to set their default values to the http proxy variables values.

Do we want to reuse, for the HTTPS mode, the same configuration as for the HTTP mode?
Well, it depends on the :term:`context`. 

We have added a new variable, named `use_for_https` here:

.. confval:: use_for_https
   :type: `boolean`
   :default: `true`

   This is a setting that enables to reuse or not the HTTP proxy configuration for HTTPS

The variable that drives the hidden/show behavior is the `use_for_https` variable because the `hidden` property has 
a `variable` target parameter that points to it: `variable: _.use_for_https`.

.. prerequisites:: Reminder

   The underscore and the point before the variable (`_.use_for_https`) points to the variable that lives in the parent 
   family.

.. questions:: Question: how does it work? 

   How will this variable drive the reuse of HTTP data to HTTPS data?

With this :confval:`use_for_https` boolean variable, there are two possibilities, and only two: 

- The http proxy's configuration will be reused for the https proxy's configuration
- The http proxy's will not be reused for the https proxy's configuration

.. questions:: Question: shall we use the `disabled` property here?

   Is it relevant to use the :term:`disabled property <disabled>` here? 
   
   **answer**: No! Because we *need* to use these variables at any :term:`context` of the proxy's manual configuration use case, 
   we simply have to point their values ​​in one direction or another depending on this or that context,
   that's why it is absolutely not a question of disabling them. The `manual.https_proxy.address` 
   and the `manual.http_proxy.port` variables shall not be disabled in the manual mode. 

Here is an example with different user values for handling HTTP and HTTPS:

.. extinclude:: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/commit/v1.1_053/config/01/config.yml
   :linenos:
   :language: yaml
   :caption: User datas in the user data file :file:`config/01/config.yml` with `use_for_https` as false

..
    ---
    proxy_mode: Manual proxy configuration
    manual:
      http_proxy:
        address: http.proxy.net
        port: 3128
      use_for_https: false
      https_proxy:
        address: https.proxy.net

If we launch the Rougail CLI: 

.. raw:: html
   :class: terminal
   :url: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/commit/v1.1_053/config/01/cmd_ro.txt

.. 
    rougail -m firefox/ -u yaml -yf config/01/config.yml

We have this output: 

.. raw:: html
   :class: output
   :url: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/commit/v1.1_053/config/01/output_ro.html
   
..
    <pre>╭────────────── Caption ───────────────╮
    │ Variable <span style="color: #ffd700">Default value</span>               │
    │          <span style="color: #00aa00">Modified value</span>              │
    │          (⏳ Original default value) │
    ╰──────────────────────────────────────╯
    Variables:
    <span style="color: #5c5cff">┣━━ </span>📓 proxy_mode (Configure Proxy Access to the Internet): <span style="color: #00aa00">Manual proxy </span>
    <span style="color: #5c5cff">┃   </span><span style="color: #00aa00">configuration</span> ◀ loaded from the YAML file "config/01/config.yml" (⏳ No 
    <span style="color: #5c5cff">┃   </span>proxy)
    <span style="color: #5c5cff">┗━━ </span>📂 manual (Manual proxy configuration)
    <span style="color: #5c5cff">    </span><span style="color: #5c5cff">┣━━ </span>📂 http_proxy (HTTP Proxy)
    <span style="color: #5c5cff">    </span><span style="color: #5c5cff">┃   </span><span style="color: #5c5cff">┣━━ </span>📓 address (HTTP address): <span style="color: #00aa00">http.proxy.net</span> ◀ loaded from the YAML 
    <span style="color: #5c5cff">    </span><span style="color: #5c5cff">┃   </span><span style="color: #5c5cff">┃   </span>file "config/01/config.yml"
    <span style="color: #5c5cff">    </span><span style="color: #5c5cff">┃   </span><span style="color: #5c5cff">┗━━ </span>📓 port (HTTP Port): <span style="color: #00aa00">3128</span> ◀ loaded from the YAML file 
    <span style="color: #5c5cff">    </span><span style="color: #5c5cff">┃   </span><span style="color: #5c5cff">    </span>"config/01/config.yml" (⏳ 8080)
    <span style="color: #5c5cff">    </span><span style="color: #5c5cff">┣━━ </span>📓 use_for_https (Also use this proxy for HTTPS): <span style="color: #00aa00">false</span> ◀ loaded from 
    <span style="color: #5c5cff">    </span><span style="color: #5c5cff">┃   </span>the YAML file "config/01/config.yml" (⏳ true)
    <span style="color: #5c5cff">    </span><span style="color: #5c5cff">┗━━ </span>📂 https_proxy (HTTPS Proxy)
    <span style="color: #5c5cff">    </span><span style="color: #5c5cff">    </span><span style="color: #5c5cff">┣━━ </span>📓 address (HTTPS address): <span style="color: #00aa00">https.proxy.net</span> ◀ loaded from the YAML 
    <span style="color: #5c5cff">    </span><span style="color: #5c5cff">    </span><span style="color: #5c5cff">┃   </span>file "config/01/config.yml"
    <span style="color: #5c5cff">    </span><span style="color: #5c5cff">    </span><span style="color: #5c5cff">┗━━ </span>📓 port (HTTPS Port): <span style="color: #ffd700">8080</span>
    </pre>

Notice that we have a `use_for_https` new variable, this variable is a `boolean` type, its default value is `True`.
We want to offer the possibility of providing an identical or possibly different proxy configuration for the HTTP and for the HTTPS protocols. 

Here is an example with identical HTTP and HTTPS proxy configuration:

.. extinclude:: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/commit/v1.1_053/config/02/config.yml
   :linenos:
   :language: yaml
   :caption: User datas in the user data file :file:`config/02/config.yml` with `use_for_https` as true

..
    ---
    proxy_mode: Manual proxy configuration
    manual:
      http_proxy:
        address: http.proxy.net
        port: 3128
      use_for_https: true

Let's launch the Rougail CLI:

.. raw:: html
   :class: terminal 
   :url: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/commit/v1.1_053/config/02/cmd_ro.txt

.. 
    rougail -m firefox/ -u yaml -yf config/02/config.yml

We have this output: 

.. raw:: html
   :class: output
   :url: https://forge.cloud.silique.fr/stove/rougail-tutorials/raw/commit/v1.1_053/config/02/output_ro.html
   
.. 
    <pre><span style="font-weight: bold; color: #ff0000">🛑 Caution</span>
    <span style="color: #ff0000">┗━━ </span>manual (Manual proxy configuration)
    <span style="color: #ff0000">    </span><span style="color: #ff0000">┗━━ </span>https_proxy (HTTPS Proxy)
    <span style="color: #ff0000">    </span><span style="color: #ff0000">    </span><span style="color: #ff0000">┗━━ </span>address (HTTPS address): <span style="color: #ff0000">🛑 mandatory variable but is inaccessible </span>
    <span style="color: #ff0000">    </span><span style="color: #ff0000">    </span><span style="color: #ff0000">    </span><span style="color: #ff0000">and has no value</span>
    </pre>

Which is logical, HTTPS proxy variables have no values set yet. 
We are going to see how to point HTTPS variables to HTTP variables.

.. keypoints:: Key points progress

    **summary**
    
    We have now the ability to build *contextual settings*:

    - if the `proxy_mode` variable's value is not `'Manual proxy configuration'` the `manual` family is disabled
    - if the `proxy_mode` variable's value is `'Manual proxy configuration'` then the `manual` family is enabled
    - if the `use_for_https` variable's value is `true`, the HTTP configuration will be reused in the HTTPS situation 
      and the `https_proxy` familiy will be hidden
    - if the `manual.https_proxy.address` has no value set, the defaut value is the same as the `manual.http_proxy.address`'s value
      (same behavior with the HTTP port and the HTTPS port variable)
      
    And yes, we did it. We have arrived at the end of the proxy's manual configuration's section.

    **Keywords**
    
    - We now know what a *property* is, we have seen in details the :term:`disabled` property,
    - We can target a variable's value in the `disabled` property's value,
      we call it a variable based contextual disabled family,
    - The :term:`hidden` property can be set to a family,
    - The fact that a property can be set dynamically,
    - The conditional dependency of a `hidden` property can depends on a `boolean` variable,
    - We know what a calculated default value is.