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I notice that this topic has not really been explored and I feel it is important to bring it up.
People generally use the text editor that comes with their system whether it is a mac or a pc those editors are not good enough for editing certain files.
The mac editor TextEdit is good for simple text or rich text editing but it lacks many capabilities and can render your files useless or insert unwanted elements or white space. The same can be said for NotePad that comes with windows.
If you are going to be editing Vanilla themes, you will run into problems editing a tpl by using the editors I mentioned above. You need to use a good text editor that can handle all types of files. Some even have error detection so you can learn how to fix errors when you edit.
I personally use SublimeText , which is free to try and costs around $75 dollars. I think it is worth every penny because of the way it has helped me learn what I am doing right and what I am doing wrong so I can fix things faster. It is easy to read and has line numbers.
Here is a list of free editors
Here is a list of the best editors money can buy