user22057: I usually use in-text citations putting the linked text in square brackets followed by the link in normal brackets. This prevents the link showing. However for a recent post I thought I would use numbering and group the links at the end. (All links related to other SE posts.) According to the edit Help the format for this is text in square brackets followed by number in square brackets. When I did this the first link immediately referred to the source of the first image I had on the page, which uses a similar system.
Am I doing something wrong? If so what? If not, is there a work-around?
Example
The instructions for linking are shown in the screenshot below:

which is marked up as:
 [1]: https://i.stack.imgur.com/yNx2e.png

Now if I add a link to the page this is on marked up as:
[a link to the page this is on][1]

typing at the bottom:
[1]: https://biology.meta.stackexchange.com/editing-help

kills the image link. I also do not see the reference number.
Now I am trying to link using Roman numerals:
[using Roman numerals][i]

This works in that it gives a link that doesn't kill the image. But this is not what I had in mind. I see I misunderstood. Will answer my own question.

user22057: So this is what I wanted to do and how I realize I need to do it.
Example
The Stack Exchange Editing Help1 shows you how to link text to external URLs.

(Biology Stack Exchange also has its own Help Center2.)
RERERENCES
1 Stack Exchange Editing Help
2 Stack Exchange Biology Help Center
Explanation
This method uses ‘dead’ reference numerals in the text and marks up the links to descriptive text in (for me) the normal way inline, but as endnotes. Rather than superscripts I could have used other brackets — (1) or {1} — but not square brackets — [can’t put 1 here] — as these clash with the image links.
Code:
<sup>1</sup> [Stack Exchange Editing Help](https://biology.meta.stackexchange.com/editing-help)
<sup>2</sup> [Stack Exchange Biology Help Center](https://biology.stackexchange.com/help)


user15950: Links and images share the same Markdown reference system. That means your references must be unique; if you use [1] for a link, you can't use [1] for another image.
Note that the references don't need to be numbers: if you format your link as [This is a link to Wikipedia][Wikipedia] and include [Wikipedia]: https://en.wikipedia.org/ at the end of the post, it will work as well:
This is a link to Wikipedia

22057: <p>I usually use in-text citations putting the linked text in square brackets followed by the link in normal brackets. This prevents the link showing. However for a recent post I thought I would use numbering and group the links at the end. (All links related to other SE posts.) According to the edit Help the format for this is text in square brackets followed by number in square brackets. When I did this the first link immediately referred to the source of the first image I had on the page, which uses a similar system.</p>
<p>Am I doing something wrong? If so what? If not, is there a work-around?</p>
<p><strong>Example</strong></p>
<p>The instructions for linking are shown in the screenshot below:</p>
<p><a href="https://i.stack.imgur.com/yNx2e.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/yNx2e.png" alt="Screenshot of link help" /></a></p>
<p>which is marked up as:</p>
<pre><code> [1]: https://i.stack.imgur.com/yNx2e.png
</code></pre>
<p>Now if I add <a href="https://i.stack.imgur.com/yNx2e.png" rel="nofollow noreferrer">a link to the page this is on</a> marked up as:</p>
<pre><code>[a link to the page this is on][1]
</code></pre>
<p>typing at the bottom:</p>
<pre><code>[1]: https://biology.meta.stackexchange.com/editing-help
</code></pre>
<p>kills the image link. I also do not see the reference number.</p>
<p>Now I am trying to link <a href="https://biology.meta.stackexchange.com/editing-help">using Roman numerals</a>:</p>
<pre><code>[using Roman numerals][i]
</code></pre>
<p>This works in that it gives a link that doesn't kill the image. But this is not what I had in mind. I see I misunderstood. Will answer my own question.</p>
 22057: <p>So this is what I wanted to do and how I realize I need to do it.</p>
<p><strong>Example</strong></p>
<p>The Stack Exchange Editing Help<sup>1</sup> shows you how to link text to external URLs.
<a href="https://i.stack.imgur.com/5crMy.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/5crMy.png" alt="Text link help" /></a></p>
<p>(Biology Stack Exchange also has its own Help Center<sup>2</sup>.)</p>
<p>RERERENCES</p>
<p><sup>1</sup> <a href="https://biology.meta.stackexchange.com/editing-help">Stack Exchange Editing Help</a></p>
<p><sup>2</sup> <a href="https://biology.stackexchange.com/help">Stack Exchange Biology Help Center</a></p>
<p><strong>Explanation</strong></p>
<p>This method uses ‘dead’ reference numerals in the text and marks up the links to descriptive text in (for me) the normal way inline, but as endnotes. Rather than superscripts I could have used other brackets — (1) or {1} — but <em>not</em> square brackets — [can’t put 1 here] — as these clash with the image links.</p>
<p>Code:</p>
<pre><code>&lt;sup&gt;1&lt;/sup&gt; [Stack Exchange Editing Help](https://biology.meta.stackexchange.com/editing-help)
&lt;sup&gt;2&lt;/sup&gt; [Stack Exchange Biology Help Center](https://biology.stackexchange.com/help)
</code></pre>
 15950: <p>Links and images share the same Markdown reference system. That means your references must be <strong>unique</strong>; if you use <code>[1]</code> for a link, you can't use <code>[1]</code> for another image.</p>
<p>Note that the references don't need to be numbers: if you format your link as <code>[This is a link to Wikipedia][Wikipedia]</code> and include <code>[Wikipedia]: https://en.wikipedia.org/</code> at the end of the post, it will work as well:</p>
<p><a href="https://en.wikipedia.org/" rel="nofollow noreferrer">This is a link to Wikipedia</a></p>
