By AppleInsider Staff

Published: 02:00 PM EST

Apple Inc. is in the latter development stages of what could possibly be its most significant 'dot release' of Mac OS X ever.

Due out next month as Mac OS X 10.5.2, the update will deliver to users of the company's Leopard operating system nearly 100 code corrections and enhancements, people familiar with the software say.

Among them are twenty new fixes that turned up as part of Mac OS X 10.5.2 build 9C16, which was released privately to developers during last week's Macworld Expo. Some of the more prominent fixes in that build target problems with resuming Time Machine backups and previewing PDF, image and mail attachments.

Since seeding the first pre-release copies of the Leopard update in mid-December, Apple has asked that its developer community test the release quite broadly. The latest build arrived without exception, maintaining a list of thirty seven core focus areas that swapped out an emphasis on 802.11 wireless testing for that of Active Directory.

Mac OS X 10.5.2, which in its current incarnation includes just two known issues, will also deliver support for Apple's just-announced Time Capsule backup appliance and include a revised version of the company's "Stacks" desktop feature.

Apple is also simultaneously testing a similar update for users of Leopard Server, which currently carries a list of nineteen core focus areas and includes over 30 specific code corrections.

Delta -- or bare bones -- versions of both Mac OS X 10.5.2 client and server are some of the heftiest yet out of Apple for a "dot release," weighing in at 450.8MB and 454.5MB, respectively.