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Any text editor can be used. The .ipt files are just text files.
Personally I use Notepad++. It's free, https://notepad-plus-plus.org/ The only downside is you need to close IPP and reopen it to see the results of your changes.
In addition to not closing when you press ctrl-x (which happens to me constantly!), it also has optional wordwrap, line numbers, and you can define a "language" which will color-code and otherwise format the text for keywords and symbols.
Here's my current language settings for IPP. This is not an .ipt file, I just changed the extension so I could upload it. Change the extension to .xml, then in Notepad++ go on the menu to Language/Define Your Language, and click the Import button. I think it will automatically recognize .ipt files but you can also change the setting by going on the menu to Language and picking the appropriate language. Imported and custom ones will appear at the bottom.
That xml file for Notepadd++ is just what I was looking for. Many thanks