maint(pat modal): Document panel-header-content.

Author: thet

src/pat/modal/documentation.md

@@ -15,8 +15,9 @@ This will load the page at `/status/server1`, extract the element with id `conte
 
 You can customise the behaviour of modals through options in the `data-pat-modal` attribute.
 
-| Property     | Default value   | Values                       | Description                                                                                             | Type                                                   |
-| ------------ | --------------- | ---------------------------- | ------------------------------------------------------------------------------------------------------- | ------------------------------------------------------ |
-| `class`      |                 |                              | A class name to be applied to the modal.                                                                | String.                                                |
-| `closing`    |  "close-button" |  ["close-button", "outside"] | Show a "close" button for closing the modal, or let it be closed by clicking outside of the modal area. | One of the mutually exclusive available string values. |
-| `close-text` |  "Close"        |                              | Specify a custom string for the close button.                                                           | String.                                                |
+| Property               | Default value           | Values                       | Description                                                                                                                                     | Type                                                   |
+| ---------------------- | ----------------------- | ---------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------ |
+| `class`                |                         |                              | A class name to be applied to the modal.                                                                                                        | String.                                                |
+| `closing`              |  "close-button"         |  ["close-button", "outside"] | Show a "close" button for closing the modal, or let it be closed by clicking outside of the modal area.                                         | One of the mutually exclusive available string values. |
+| `close-text`           |  "Close"                |                              | Specify a custom string for the close button.                                                                                                   | String.                                                |
+| `panel-header-content` |  `:first:not(.header)`  |  CSS selector or "none"      | Specify a CSS selector which is used for the modal header. If set to "none" no header will be added automatically and you can provide your own. | String.                                                |