Okay, I might sound lazy. When trying to copy mixture of text and latex formulas in an answer, it is always easy. I can simply click "edit" and copy the source. But when trying to do the same in a comment, either others' comment or my own comment after 5 minutes since it was posted, I can copy the source of each latex formula by "Show Source" of MathJax, but when there are more than one latex formula and/or also text to copy, doing this for each part isn't so simple. So I wonder if there is some easy way? Thanks and regards!
I do not know whether I am supposed post this here - since this is tagged feature-request and I am not writing about a new feature. But I think there is quite a simple workaround - when you are viewing the question in your browser, choose View Source (Ctrl+U in Firefox).
You can copy the comments (including dollars) from there. You can search the source for comment or the name of the user, who posted it.
As an example, I've copied the following comments from one of your questions:
If the poster of comment used link in his comments and you paste the text of the comment from the source, the link is not displayed unless you delete rel="nofollow". Formatting (bold, italics) seems to be copied well.
A few more experiments:
Comment containing formatting (italics) from here:
Comment containing colors from here:
Probably there are many further problems which can arise with using this method - such as folded comments mentioned by Tim.
Maybe someone will suggest a more straightforward way. The only thing I was able to do was using StackPrinter where all comments are unfolded. I chose the question, but did not print it and instead of printing I viewed the source of the page. From there I was able to copy the comment. E.g. from here I copied the following
Maybe there is a simple way how to display a question (or an answer) with all comments unfolded, but I am unaware of it.
Note that from the source you can also read comment id, which can be used to link directly to the comment in this format: "Show by direct substitution..."
EDIT: Comment id and link to a comment can now be obtained simply by clicking on it, see How to link to a comment?
I got sufficiently tired of comment-copying problems to make a bookmarklet Copy all comments to answer box. When used on a question page, the bookmarklet copies all comments under the question to the answer box.
For example, I used it on the Batman question:
The inserted text does not get rendered in the editor's preview window until you modify it, e.g., adding a space.