The true nature of Excel workbooks - zipped files

Trivia question: what format do Excel workbooks use?  If your answer is a proprietary Microsoft format, you couldn't be further from the truth.

Let's create a simple Excel workbook and dissect it:

A simple workbook containing 3 sheets

Here's what this looks like in Windows Explorer:

The workbook above.

So far, so what.  But let's now change the file extension from .xlsx to .zip (ignoring any complaints from Microsoft):

You can now see that the workbook is actually a collection of zipped files.

When you double-click on the file now, you can see its true contents:

The true contents of the workbook: the worksheets folder contains one XML file for each worksheet.

Here's a sample of the first worksheet:

The XML underlying each worksheet is completely transparent.

As Michael Caine apparently didn't say: "Not a lot of people know that!".