> Browser bookmarks are actually not the same as the bookmarks I keep in LinkAce

You are not alone, I currently use Diigo with the same needs; the Diigo bookmark list is massive, unwieldy, goes back decades - the in-browser bookmarks are slimmmed down to just what I use commonly. What we really need is a new RFC "LinkDav" which follows in the footsteps of CardDav, CalDav and WebDav to round out our data portability lives. Want to try your hand at writing a RFC? :-)

On the Import docs section it just says "...in the HTML format" - there's a Chrome, Firefox and IE version of HTML Export from Diigo, it would be helpful to understand which one would be the best for import to LinkAce: https://www.diigo.com/tools/export

There is a standard already, called OPML that is already used in every RSS reader to store a list of feeds. Being XML behind, I'm sure it can be adapted to contain everything related to a bookmarking service; it's not a complete format like CalDAV and friends, but it looks like a solid base to build on.

OPML (I am familiar) could be used as a basis yep, but it's a file format which is more akin to vCard, vCal and iCal - CalDav, CardDav and WebDav are the transport(?) layers (API layers, operational layers, call them what you will) which sit on top of the file format standards providing the interoperability.

> I use browser bookmarks for regularly accessed sites and have a separate application that takes care of all those links I would like to “keep in mind” but don’t want to pollute my browser bookmarks with

I strongly feel like it could be both. You created something that does one thing (I assume) really well. Adding sync may sound like too much on top but we already are living in a world of isolated data islands, it may be a good idea to start building bridges.

Maybe sync browser bookmarks in, mark them with a special tag, and only sync those out.