When reindexing, virtually every dynamically generated page is coming back as "modified" each time, although no information should be changing in these pages at all, and there's no date/time in the pages or anything else that might be changing. Why?

Alkaline appends an If-Modified-Since field with the most recent date of the file for each reindex query to the web server, which is compliant to the HTTP RFC. The server does not know whether the page has changed or not, and will always generate a full copy. Thus, it does not reply to Alkaline with a Not Modified error code, but with a full new page. In respect to that, Alkaline will fully reindex the page and will not use a previously known MD5 signature to check the contents changes.

Alkaline will subsequently do an MD5 checking for previously available content. You will see [md5-unch] when a document hasn't changed. A dynamic page, for example, will still be retrieved but it will not be reindexed saving some processor time.