[emellaich]

I think there may be a solution on the way that will allow us to create tags/categories for non-DRM books on the Kindle.

I had an idea that I ran by kovidgoyal, and he tells me that he will add it into version 0.6 of calibre. I've done some testing of my own and it looks like it will do the job for us.

Calibre already allows you to tag books in its library. Calibre also allows you to write books to mobi format. So, my request was to add the list of tags directly to the book content.

With the Kindle search function we can then search for the tags and find books that have those tags. Of course, adding content to existing books will only work for books that do not have DRM.

I did some testing by creating a file with keywords with it in order to see how this would work. First, I noted that we couldn't simply search for a word because it would find the tagged instances and non-tagged versions. For example, if I search for "Help" it will find the word "help" every time it is used in every book.

If you want to specifically search for tags, you will need to make them unique. I wanted to surround tags by delimiters like this /tag1/help/tag3/. Unfortunately, if you search for "/help/" then the Kindle will ignore the non-text characters and it will find every instance of the word "help" in every book.

The next idea I came up with was to use letters as the delimiters. For example, using ttt as a delimiter, a book might have a tag string as follows:
tttScience FictiontttMysteryttthelpttt

Unfortunately, it seems that the Kindle only indexes complete words, and in the case above it doesn't see the word Mystery as a complete word. Finally, I tried using a delimiter of "tt tt". Using this approach the string of tags from the example above would be:
tt ttScience Fictiontt ttMysterytt tthelptt tt

This worked great!! I have 640 books, and when I search for ttMysterytt it only finds my test book. I also tried Science Fiction since it was a tag with an embedded space. In this case, it had no problem finding "ttScience Fictiontt" in only my test book.

When I described this feature to kovidgoyal, I asked him to let the tag delimiter be user settable, and to allow multiple characters because I knew it was going to take something tricky like the solution above.

So, if this works as I expect it to we now have tags on our Kindle!! With two caveats, of course:

1) You'll need to use calibre to manage your library (no pain here -- thanks again kovidgoyal).

2) It'll only work on DRM-free books.

Michael