I guess you can use API for both. You can use an XML reader to read the output of API and paste it in the format you like the most.

I've read the API documentation, and API is useful for what I need, but I still want these options for Allpages and Prefixindex, because API is not that easy and not everyone knows API (like me, until now :p). The normal in-wiki Special:Prefixindex with more options is still much easier and better than API, imo.

ayg wrote:

I don't think we need to add more formatting options for the sole purpose of copy-pasting. Get a text editor with multiline regex search and replace, and do something like

s/\t/\n/;s/^/Template:/

(depending on how copy-pasting three-column tables renders in plaintext with your browser/OS, I assumed the cell boundaries would become tabs).

conrad.irwin wrote:

Relatedly, I'd like an option to give me back the columns when I visit the page "Special:AllPages/Example", I find the extra click on "Example" annoying - I am using AllPages like that because I want to see the categories near that name.

Closing per #3

ddm wrote:

it would be very useful to be able to specify the number of columns in the output table when using Special:PrefixIndex and looking at the code, this seems to be a trivial addition. I can provide a patch if there's interest.

To support something like this:
{{Special:PrefixIndex/{{FULLPAGENAME}}/|columns=2}}

ddm: New ticket welcome.

ddm wrote:

created new ticket: bug 60759