Patch files packing/unpacking format

They are like custom zip files, or something like that. Check this extractor, it has a script for cxl patch files. Maybe you can get some info from it:

http://aluigi.altervista.org/quickbms.htm

 

are you after the actual tool? I believe there are a couple different ones.
I use this one here - http://www.generation-city.com/citiesxl/pakunpak/Download.php


Features

• Unpak of a file or of a folder of Pak, Patch, Lvl, Sol, Sgbin files.
• Pak of a folder data\... in a Patch file.
• Unpak of a SGBIN file with automatic conversion of MC-DDS files into DDS standards and editable.
• Duplication of objects thanks to the compression SGBIN which redeploys DDS to MC-DDS and offers you to enter a new name for the object. You can so duplicate an object, change its textures and its properties.
• Explorer allows you to show all unpaked data in the preview window. It shows game graphics and texts with the possibility to configure external editors (text and graphic) to edit them more easily with a simple right click.
• Export / Backup of your cities (Save game) with creation of a text file which contains the list of your mods installed to return easier the distribution of your city online. (If a mod was used for a city, it will be necessary on another computer to open this city)
• Import: up to 10 cities are possible to be imported on Slots added for this occasion to not replace the official maps. A (playable) map "Plat-Pays" was added with that end in view, two by region for firsts 5 regions. It is on these maps that will be imported cities.
• This help file which will become rich progressively, with tutorials..
• A link "Check for updates"
• Other improvements will follow: (Easy Addition of new maps (9 maximum) in the region "Generation City",

 

so what are you trying to do or achieve?