Kludge to use IMPORTRANGE with INDIRECT in Google Sheets

The correct kludgey way to use IMPORTRANGE combined with an INDIRECT in Google Sheets, to dynamically grab data (which can be a cell, a cell range, or basically an entire sheet if you use a huge range). Stumbled upon completely accidentally after hours of searching; thanks completely obtuse Google documentation!

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=IMPORTRANGE("[key]", "[]"&INDIRECT("[function]") )

* don't include the []

[key] = key to your other spreadsheet, which is shown in the URL.
[] = just some blank space in quotes, or can be any fixed part of the function which doesn't change (eg a preceeding column letter). This appears necessary to satisfy the app that you are indeed providing it some string. You can't just use INDIRECT on its own as it errors out.

[function] = whatever you want to do to bring in the cell reference for the second sheet.

eg. INDIRECT( "A"&SUM(B1:B10) )

Whatever you put inside the INDIRECT("") must obviously produce a cell reference to a cell on your current sheet, and in that cell you can do whatever you like to produce ANOTHER cell reference (this time, the one referring to your separate data sheet).