api_docs: Better structure Image previews section.

api_docs/changelog.md

@@ -866,7 +866,7 @@ deactivated groups.
 
 **Feature level 336**
 
-* [Markdown message formatting](/api/message-formatting#image-previews): Added
+* [Markdown message formatting](/api/message-formatting#images): Added
   `data-original-content-type` attribute to convey the type of the original
   image, and optional `data-transcoded-image` attribute for images with formats
   which are not widely supported by browsers.
@@ -1435,7 +1435,7 @@ deactivated groups.
 **Feature level 287**
 
 * [Markdown message
-  formatting](/api/message-formatting#image-previews): Added
+  formatting](/api/message-formatting#images): Added
   `data-original-dimensions` attributes to placeholder images
   (`image-loading-placeholder`), containing the dimensions of the
   original image. This change was also backported to the Zulip 9.x
@@ -1511,7 +1511,7 @@ releases.
 **Feature level 278**
 
 * [Markdown message
-  formatting](/api/message-formatting#image-previews): Added
+  formatting](/api/message-formatting#images): Added
   `data-original-dimensions` attributes to placeholder images
   (`image-loading-placeholder`), containing the dimensions of the
   original image. Backported change from feature level 287.
@@ -1524,7 +1524,7 @@ No changes; feature level used for Zulip 9.0 release.
 
 **Feature level 276**
 
-* [Markdown message formatting](/api/message-formatting#image-previews):
+* [Markdown message formatting](/api/message-formatting#images):
   Image preview elements not contain a `data-original-dimensions`
   attribute containing the dimensions of the original image.
 

api_docs/message-formatting.md

@@ -121,10 +121,10 @@ the href for those is the default behavior of the link that also
 encodes the channel alongside the data-stream-id field, but clients
 can override that default based on `web_channel_default_view` setting.
 
-## Image previews
+## Images
 
 When a Zulip message is sent linking to an uploaded image, Zulip will
-generate an image preview element with the following format.
+generate an image preview element with the following format:
 
 ``` html
 <div class="message_inline_image">
@@ -136,6 +136,8 @@ generate an image preview element with the following format.
 </div>
 ```
 
+### Image-loading placeholders
+
 If the server has not yet generated thumbnails for the image yet at
 the time the message is sent, the `img` element will be a temporary
 loading indicator image and have the `image-loading-placeholder`
@@ -168,6 +170,8 @@ backlogged, an individual message containing multiple image previews
 may be re-rendered multiple times as each image finishes thumbnailing
 and triggers a message update.
 
+### Recommended client processing of image previews
+
 Clients are recommended to do the following when processing image
 previews:
 
@@ -217,16 +221,18 @@ previews:
   format match what they requested.
 - No other processing of the URLs is recommended.
 
-**Changes**: In Zulip 10.0 (feature level 336), added
+### Changes to image formatting
+
+**In Zulip 10.0** (feature level 336), added
 `data-original-content-type` attribute to convey the type of the
 original image, and optional `data-transcoded-image` attribute for
 images with formats which are not widely supported by browsers.
 
-**Changes**: In Zulip 9.2 (feature levels 278-279, and 287+), added
+**In Zulip 9.2** (feature levels 278-279, and 287+), added
 `data-original-dimensions` to the `image-loading-placeholder` spinner
 images, containing the dimensions of the original image.
 
-In Zulip 9.0 (feature level 276), added `data-original-dimensions`
+**In Zulip 9.0** (feature level 276), added `data-original-dimensions`
 attribute to images that have been thumbnailed, containing the
 dimensions of the full-size version of the image. Thumbnailing itself
 was reintroduced at feature level 275.