I think that Youtrack should let the users to highlight one or more rows in a code block, because IMHO it would allow to show where a problem resides in a even better way.
I have made a mock-up image to show you what I mean. In the example, I want to make someone notice that in a block of code there's an unnecessary "span" tag; to do this I want to highlights the opening and the closing "span" tag, so when someone will see the code block he or she will understand better what I'm thinking is wrong.
In order to do that, you may add a new tag that could work inside a code block and would allow to highlight the current row.
I have written a very short example of how I think you may implement this feature in code; to avoid having the text converted by YouTrack I have written the last "code" tag with a ] instead of using }
{code:lang=whatever}
row1
row2
{highlight:yellow}row3{highlight}
row4
row5
{code]If you can't do this because it's too complicated or too time-consuming, at least allow to show line numbers in a code block, so I could write in a issue report "Have a look at lines 3 and 8 in the code shown below" and be more specific.
To express better what I mean for example, if I write:
{code:first-line=1}
row1
row1-1
row2
row3
row3-1
row3-2
row3-3
row4
row5
row5-1
{code]I would like to see this appearing this way:
1: row1
2: row1.1
3: row2
4: row3
5: row3.1
6: row3.2
7: row3.3
8: row4
9: row5
10: row5.1