docs: improve syntax guides

docs/reference/index.rst

@@ -19,3 +19,4 @@ Contents
    default-extensions
    rst-syntax
    myst-syntax
+   syntax

docs/reference/myst-syntax.md

@@ -350,6 +350,9 @@ For internal references, both Markdown and MyST syntax are supported. In most ca
 should use MyST syntax though, because it resolves the link text automatically and gives
 an indication of the link in GitHub rendering.
 
+For referencing pages from other documentation sets, you can use
+{ref}`Intersphinx <how-to-link-docs-intersphinx>``.
+
 (a_section_target_myst)=
 
 #### Referencing a section
@@ -378,11 +381,6 @@ or title for the targeted element, you must specify a link text.
 * - `` {ref}`link text <a_random_target_myst>` ``
   - {ref}`link text <a_random_target_myst>`
   - References a target and specifies a title.
-* - `` {ref}`project_key:an_external_target` ``
-  - Default link text
-  - You can also reference targets in other Sphinx projects. `project-key` must be a key
-    in the `intersphinx_mapping` dictionary in `conf.py`. The link text defaults to the
-    target's title.
 * - ``[`xyz`](a_random_target_myst)``
   - [`xyz`](a_random_target_myst)
   - Use Markdown syntax if you need markup on the link text.

docs/reference/rst-syntax.rst

@@ -415,7 +415,8 @@ To override the title, add the ``:title:`` option.
 Internal references
 ~~~~~~~~~~~~~~~~~~~
 
-You can reference pages and targets in this documentation set, and also in other documentation sets using Intersphinx.
+You can reference pages and targets in this documentation set. For referencing pages from other documentation sets,
+you can use :ref:`Intersphinx <how-to-link-docs-intersphinx>`.
 
 
 .. _a_section_target:
@@ -447,9 +448,6 @@ You can add targets at any place in the documentation. However, if there is no h
    * - ``:ref:`Provided link text <a_random_target>```
      - :ref:`Provided link text <a_random_target>`
      - References a target and specifies a title.
-   * - ``:external+project_key:ref:`an_external_target```
-     - Default link text
-     - You can also reference targets in other Sphinx projects. ``project-key`` must be a key in the ``intersphinx_mapping`` dictionary in ``conf.py``. The link text defaults to the target's title.
 
 Adhere to the following conventions:
 
@@ -473,10 +471,6 @@ If a documentation page does not have a target, you can still reference it by us
      - :doc:`index`
    * - ``:doc:`Provided link text <index>```
      - :doc:`Provided link text <index>`
-   * - ``:external+project_key:doc:`howto/index```
-     - Default link text (from document title)
-   * - ``:external+project_key:doc:`Provided link text <how-to/index>```
-     - Provided link text
 
 Adhere to the following conventions:
 
@@ -488,9 +482,6 @@ Adhere to the following conventions:
   changes.
 - Never "override" the link text with the same text that would be generated
   automatically.
-- When using an external target, ``project_key`` must be a key in the
-  ``intersphinx_mapping`` dictionary in ``conf.py``.
-
 
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