How does this macro work to download a binary file?

[leeand00]

\define download-xlsx-tiddler(title,caption)
<a href={{{ [[data:application/vnd.openxmlformats-officedocument.spreadsheetml.sheet;base64,]addsuffix{$title$}] }}} download="$title$">$caption$</a>
\end

It's called like this:

<<download-xlsx-tiddler "Presidents and Justices.xlsx" "Presidents and Justices.xlsx">>

I see that it mentions the MIME type of the and the base64 format is also mentioned, but I don't think I really understand it.  It looks like it's using transclusion and a filter, but I don't really understand the "data:" portion and where the documentation for that is...but it's really neat as it means you can store any sort of file in a Tiddlywiki 5 and download it with a link.

Thanks!

[Jed Carty]

One way browsers get around handling incompatible data types is to convert them into a base 64 representation that uses only basic ascii characters. Tiddlywiki encodes non-text tiddlers in the same way. Browsers can, give the correct mime type, treat the base64 encoded string as though it were binary data for common data types. So to download the binary versions of the base64 encoded file you can create a download link that points to the base64 encoded string with the proper prefix describing the mime type and encoding and it will download the binary file. The macro creates a link that does exactly that, so when you click on it you get prompted to download the file.

[leeand00]

So,

<a href={{{ [[data:<MIME-TYPE>;<Binary-ENCODING>,]addsuffix{<tiddler-title>}] }}} download="<tiddler-title>"><link-title></a>





is what it really means?  Am I correct?  Apologies, I guess I wasn't clear that this question was about the syntax.  But thank you, your answer did clear it up for me.  Is there any documentation regarding the data: syntax?



[Jed Carty]

It isn't a tiddlywiki thing, that is just how anchor tags work. I imagine that MDN or W3C has some information about it.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/Data_URIs

[leeand00]

Oh so I'm barking up the wrong tree!  Thanks for clearing that up and pointing me to the correct documentation.  I wasn't aware that I was looking in the wrong documentation.