Make clear images should be included in clients, and discuss future changes

proposals/4347-emoji-verification-images.md

@@ -31,7 +31,7 @@ same or different.
 I propose providing a fixed set of images to use for emoji verification, and
 recommending a fixed layout for display on screen.
 
-### Changes to the emoji table
+### Including URLs in the Emoji table
 
 Currently the spec provides Unicode code points of emoji for each
 number 0-63 along with translated names. It also provides this information as
@@ -80,6 +80,13 @@ I also propose that graphical clients SHOULD display these images in two rows,
 centred vertically, with 4 images on the first row and 3 images on the second,
 with the local translation of the corresponding word below each image.
 
+Unless absolutely necessary, the images will not change, so clients are not
+expected to update them in future, and will probably not bother to automate
+downloads of the images as part of their build process.
+
+There is no uptime guarantee for the supplied URLs, so clients SHOULD NOT depend
+on them being available when a user needs to use them.
+
 ### Non-graphical clients
 
 Non-graphical clients or other clients that are unable to use the supplied
@@ -89,8 +96,7 @@ images may continue to use Unicode code points as before.
 
 I propose taking a snapshot of the relevant images from
 [twemoji](https://github.com/twitter/twemoji) at the time of incorporating this proposal
-into the spec, and freezing the set of images at that time. (Until/unless some
-other MSC requires them to be changed.)
+into the spec, and freezing the set of images at that time.
 
 These images are attractive and clear.
 
@@ -98,6 +104,13 @@ These images are provided under the CC BY 4.0 license so may be used with
 proper attribution, which should be added to the spec text and client
 applications.
 
+### Future changes
+
+If at all possible, these images will not change. In future, if they need to
+change in an incompatible way, I expect that the verification process will be
+extended to include information allowing clients to negotiate which image set to
+use, but this is out of scope for this proposal.
+
 ## Potential issues
 
 * If existing clients use Unicode characters to aid accessibility (e.g. for