bring back section headers

doc/rtd/explanation/format.rst

@@ -46,7 +46,8 @@ Cloud config data
 | **Header:** #cloud-config
 | **Content-Type:** text/cloud-config
 
-**Example**
+Example
+-------
 
 .. code-block:: yaml
 
@@ -55,7 +56,8 @@ Cloud config data
     chpasswd:
     expire: False
 
-**Explanation**
+Explanation
+-----------
 
 Cloud-config can be used to define how an instance should be configured
 in a human-friendly format. The cloud config format uses `YAML`_ with
@@ -84,14 +86,16 @@ User data script
 | **Header:** #!
 | **Content-Type:** text/x-shellscript
 
-**Example**
+Example
+-------
 
 .. code-block:: shell
 
     #!/bin/sh
     echo "Hello World" > /var/tmp/output.txt
 
-**Explanation**
+Explanation
+-----------
 
 A user data script is a single shell script to be executed once per instance.
 User data scripts are run relatively late in the boot process, during the
@@ -105,15 +109,17 @@ Cloud boothook
 | **Header:** #cloud-boothook
 | **Content-Type:** text/cloud-boothook
 
-**Simple Example**
+Simple Example
+--------------
 
 .. code-block:: shell
 
    #cloud-boothook
    #!/bin/sh
    echo 192.168.1.130 us.archive.ubuntu.com > /etc/hosts
 
-**Example of once-per-instance script**
+Example of once-per-instance script
+-----------------------------------
 
 .. code-block:: bash
 
@@ -131,7 +137,8 @@ Cloud boothook
    fi
    sudo echo $INSTANCE_ID > $PERSIST_ID
 
-**Explanation**
+Explanation
+-----------
 
 A cloud boothook is similar to a :ref:`user data script<user_data_script>`
 in that it is a shell script run on boot. The boothook is different in that:
@@ -148,7 +155,8 @@ MIME multi-part archive
 | **Header:** Content-Type: multipart/mixed;
 | **Content-Type:** multipart/mixed
 
-**Example**
+Example
+-------
 
 .. code-block::
 
@@ -175,7 +183,8 @@ MIME multi-part archive
     - echo "this is from a cloud-config." > /var/tmp/bootcmd.txt
     --===============2389165605550749110==--
 
-**Explanation**
+Explanation
+-----------
 
 Using a MIME multi-part file, the user can specify more than one type of data.
 
@@ -242,7 +251,8 @@ Cloud config archive
 | **Header:** #cloud-config-archive
 | **Content-Type:** text/cloud-config-archive
 
-**Example**
+Example
+-------
 
 .. code-block:: shell
 
@@ -256,7 +266,8 @@ Cloud config archive
         bootcmd:
         - echo "this is from a cloud-config." > /var/tmp/bootcmd.txt
 
-**Explanation**
+Explanation
+-----------
 
 A cloud-config-archive is a way to specify more than one type of data
 using YAML. It can be seen as an alternative to building a MIME multi-part
@@ -283,7 +294,8 @@ Jinja template
 | **Header:** ## template: jinja
 | **Content-Type:** text/jinja
 
-**Example cloud-config**
+Example cloud-config
+--------------------
 
 .. code-block:: yaml
 
@@ -292,15 +304,17 @@ Jinja template
    runcmd:
      - echo 'Running on {{ v1.cloud_name }}' > /var/tmp/cloud_name
 
-**Example user data script**
+Example user data script
+------------------------
 
 .. code-block:: shell
 
    ## template: jinja
    #!/bin/sh
    echo 'Current instance id: {{ v1.instance_id }}' > /var/tmp/instance_id
 
-**Explanation**
+Explanation
+-----------
 
 `Jinja templating <https://jinja.palletsprojects.com/>`_ may be used for
 cloud-config and user data scripts. Any
@@ -319,15 +333,17 @@ Include file
 | **Header:** #include
 | **Content-Type:** text/x-include-url
 
-**Example**
+Example
+-------
 
 .. code-block:: text
 
     #include
     https://raw.githubusercontent.com/canonical/cloud-init/403f70b930e3ce0f05b9b6f0e1a38d383d058b53/doc/examples/cloud-config-run-cmds.txt
     https://raw.githubusercontent.com/canonical/cloud-init/403f70b930e3ce0f05b9b6f0e1a38d383d058b53/doc/examples/cloud-config-boot-cmds.txt
 
-**Explanation**
+Explanation
+-----------
 
 An include file contains a list of URLs, one per line. Each of the URLs will
 be read and their content can be any kind of user data format, both base
@@ -351,13 +367,15 @@ Part handler
 | **Header:** #part-handler
 | **Content-Type:** text/part-handler
 
-**Example**
+Example
+-------
 
 .. literalinclude:: ../../examples/part-handler.txt
    :language: python
    :linenos:
 
-**Explanation**
+Explanation
+-----------
 
 A part handler contains custom code for either supporting new
 mime-types in multi-part user data or for overriding the existing handlers for