What Excel is
An Excel workbook is a zip archive of XML parts describing sheets, cells, formulas, styles and charts. The .xlsx extension is that format; .xls is the older binary one from before 2007.
Finance, operations and anyone who received a file from finance or operations.
What MediaWiki is
MediaWiki table markup opens with {| and a class, marks headers with an exclamation mark and rows with |-.
Wikipedia editors and anyone running a MediaWiki install.
What changes when you convert Excel to MediaWiki
Only the first sheet is read, and cells are read as the text Excel displays rather than the number underneath. That matters for dates: a cell showing 15/03/2026 arrives as that string, not as a serial number you would then have to decode.
The wikitable class is applied, which is what gives the table borders and header shading on Wikipedia.
What carries over from Excel to MediaWiki
Excel records 3 things about a table that MediaWiki has no way to hold.
Excel distinguishes a number from the text of a number; MediaWiki does not, so every value arrives as text and has to be re-parsed by whatever reads it next.
An empty cell and a missing one are the same thing in MediaWiki, so a null and an empty string in the Excel both come out blank and can no longer be told apart.
MediaWiki marks its header cells differently from its data cells, so the first row is written with that marker.
Anything visual in the Excel - weight, alignment, colour, column widths - has no counterpart in MediaWiki and is dropped. The values are what survives.