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When you mouse over line numbers in IDEs, such as Visual Studio or Notepad++, the mouse cursor is flipped horizontally. I can't think of a reason this would be a ubiquitous user interface decision. Line numbers are already set apart from the code by colors or lines, and the cursor flip doesn't prevent the obstruction of the numbers, or make setting breakpoints easier. Does anyone know why this is a common decision?

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I think it's an affordance cue; Word does this too, for some reason. Don't know the exact reasonings though – Ben Brocka May 31 '13 at 20:24
up vote 18 down vote accepted

The first time I saw this behavior was with Office 95. Word, to this day, still does this.

Word 2010 with cursor change

In Word and Other applications like Notepad++, this cursor change indicates "a whole line" is the point of selection. Clicking while the cursor is in this state will select the entire line.

Selecting an entire line in Word 2010

Selecting an entire line in Notepad++

Selecting an entire line is especially useful activity in text editors like Notepad++ when the line can end beyond the right portion of the screen. Clicking and dragging in this space will select multiple lines. Changing the cursor gives the user a cue that some different action can be made. This invitation to click is non-destructive and explorable.

On a personal note, when the cursor does not change (e.g. Eclipse IDE), I'm frequently disappointed by the lack of this feature.

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Ah, that makes perfect sense. Thanks for the information! – Mike Precup May 31 '13 at 20:40
+1 Interesting, I never knew this. – Charles Wesley May 31 '13 at 20:44
the only downside really is that it becomes annoying to click before the first char in the line with the mouse, (a small buffer zone will fix this) – ratchet freak May 31 '13 at 20:57
@ratchetfreak I agree. That "buffer zone" exists in word, but not Notepad++. It's a simple design and coding issue that would be easily fixed, but I've never lauded N++ as a high-UX project. – mawcsco May 31 '13 at 21:01

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