The limit is 500 characters. When the message length is
> 500, the following behaviour is triggered:
Unless we reduce the length until
<= 500, we won't be able to post it.
It seems that if we add a line break to our message, that is, pressing Shift + Enter to move the cursor to the next line, we can "bypass" the 500-char limit:
The shortcoming of this approach is that the MarkDown syntax will be automatically disabled. So, if we write e.g
This is **a test**, it will be handled literally instead of converted to "This is a test".
Update (Andrew's comment): When adding a line break, SE thinks you're going to upload a code listing, or similar. That's why Markdown is disabled.
When breaking a line, an extra button appears. If we click it, it will format the whole message as a code excerpt:
If the message/code is too long, it will be displayed partially:
Then we can click the
see full text link to expand it.