The DocBook documentation suggests one can do a '''<entry align="center">'''__tick__'''</entry>''' (the triple single ticks escape from QuickBook into BoostBook). However unfortunately BoostBook defines CSS which overrides the per-cell alignment :(
How about trying <colspec align="center"> instead? If I understand the documentation right, you should put that in the table heading.
I actually stumbled across an answer to this quite by accident, and at the same time I solved how to do coloured text in Boost Quickbook. Witness the beauty of coloured and centered Quickbook text in the table at https://ci.nedprod.com/view/All/job/Boost.AFIO%20Build%20Documentation/Boost .AFIO_Documentation/doc/html/afio/design/acid_write_ordering/write_ordering_ data.html. Here's how I did it in Quickbook: [table:power_loss_safety Power loss safety matrix: What can you lose if power is suddenly lost? [[][[role aligncenter Metadata no longer matches data[footnote This doesn't mean that metadata is corrupted, this means for example that a file is said to have 100Kb but is in fact partially garbage because metadata was updated before data was fully changed on storage.]]][[role aligncenter Newly created file content corrupted]][[role aligncenter File data content rewrite corrupted]][[role aligncenter Max seconds of writes reordered without using `fsync()`]][[role aligncenter Max seconds of writes lost]]] [[[role alignright FAT32]][__tick__][__tick__][__tick__][][]] [[[role alignright ext2]][__tick__][__tick__][__tick__][[role aligncenter 5]][[role aligncenter 5]]] [[[role alignright ext3/4 `data=writeback`]][__tick__][__tick__][__tick__][[role aligncenter 5/60]][[role aligncenter 60]]] [[[role alignright ext3/4 `data=ordered` (default)]][__cross__][__cross__][__tick__][[role aligncenter 5/60]][[role aligncenter 60]]] [[[role alignright UFS + soft updates]][__cross__][__cross__][__tick__][][]] [[[role alignright HFS+]][__cross__][__cross__][__tick__][][]] [[[role alignright NTFS]][__cross__][__cross__][__tick__][][]] [[[role alignright ext3/4 `data=journal`]][__cross__][__cross__][__cross__][[role aligncenter 60]][[role aligncenter 60]]] [[[role alignright BTRFS]][__cross__][__cross__][__cross__][][]] [[[role alignright ZFS]][__cross__][__cross__][__cross__][[role aligncenter 5]][[role aligncenter 30]]] ] The key here is the [role styleclass text] modifier: this just happens to spit out <span class="styleclass">text</span>. By adding suitable extra CSS to the main CSS file, one can make coloured text, or in my case, turn a span into a display:inline-block; and therefore can do text-align:center. I hope this is useful to someone someday. If [role] will continue to always do this, and it's not just by accident, it might be worth adding to the Quickbook FAQ. That said, a proper formally specified typesetting mechanism would be a lot better again. Niall --- Opinions expressed here are my own and do not necessarily represent those of BlackBerry Inc.