how to check if selected text is inside two lines of text

We开发者_如何学运维 have text in the document and part of the text was selected by user with mouse like:

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa****aaaa   aaaaaaaaaaaaaaaaaaaaa  aaaaaaa
a aaaaaaa aaaaaaaaaaaaa aaaa****aaaaaaaa aaaaaaaaaaaaaaaaaaa aaaaaaaaaaa

How can I check if selection is only in one line or in both?

html structure is like:

<div>
   <span> aaaaaaaaaa aaaaaaaaaaa aaa <span> selectedt text </span> </span>
</div>  

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Don't know exactly what you are going for, but maybe this could help;

http://www.quirksmode.org/js/events_mouse.html

Under section 'relatedTarget, fromElement, toElement' --> when you give the span elements an id, you could check from which element you started, and in which you ended. Hereby knowing if there was a cross in elements.

I do not think that it's possible to know exactly on which line (on screen) the user starts ends, because of text wrapping, resolution, screen size, font size etc.

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That all depends on the size of the users screen/window size

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An idea could be to momentarily span one character with a force-layout tag, a span with position:relative, check the height. Then compare it with the entire selections height, retrieved the same way.