I suddenly discovered something that I haven’t seen before. I was writing in a markdown document and came to the bottom of the window, I continued to write but DT didn’t show what I was writing and I can’t scroll the source view. Here I was playing with syntax highlighting (which I haven’t managed to get to work) but the same thing happens when I just type text. Here is how it looks:
Am I missing something, or is this a bug?
This is a known issue which will be fixed by the next release.
I note you were puttig a fenced code block with python in the first line.
If you are hoping to use syntax highlighting, the correct form is language-python.
Curious question: in all other places I’ve used fenced code blocks so far the it has been
```language
Why is it different in DT? (some decision, or just a consequence of using the javascript library?)
I don’t know what other places you’re referring to but this is specifically the Prism.js syntax.
There’s
https://benborgers.com/marked-prism
and of course
They’re all showing code fences with short forms of the language (i.e. ruby instead of language-ruby). I’d wager that these are some other places 
I agree that prism.js uses language-xxxx, but that is not related to the MD renderer: it could simply prepend the language- to any xxxx it finds at the start of the code fence and pass the whole thing onto prism. I think that DT should follow the MD conventions here (see above for the Github and markdownguide links). Or it should be forgiving enough to add the language- prefix if it is missing.
We aren’t doing anything specific here except using the Prism.js extension as-is. So I suppose this would be a question for the author of Prism.
Major site - GitHub. Apps: bbedit, marked, ulysses, bear, etc.
This is literally the first time I’ve seen anything else.
+ 1
After investigating a bit… You’re of course right in that prism uses class names with a leading lang- or language-. OTOH, the MD-to-HTML converter produces this
<code class="javascript">
from this
```javascript
If, instead it would convert this start of a code fence to
<code class="language-javascript">
all would be easy-peasy. May be it’s possible to have the converter have a look at the string after the start of the code fence and adjust the class name accordingly? That would bring it more in line with the leading other MD converters, I think.