http://www.linuxfoundation.org/en/AT-SPI_on_D-Bus leads to a 'this topic does not exist. A quick search looks like https://wiki.linuxfoundation.org/accessibility/atk/at-spi/at-spi_on_d-bus may be a new page for it but not familiar enough with it to know if that page is appropriate. Wayback Machine shows the old page and it goes from working to breaking between 20016 and 2019: https://web.archive.org/web/diff/20190313003220/20161208060712/https://wiki.linuxfoundation.org/en/AT-SPI_on_D-Bus .
Searching online lead to repositories and clones with a readme still pointing to the same broken link and https://accessibility.kde.org/developer/atk.php mentioned as an additional resource which is not accessible so upstream project may need corrections and have best suggestion for new site; I have not pursued upstream communication.
Also applies to accessibility/at-spi2-core and accessibility/py-atspi