Documentation/reference for fastboot Where can I find the documentation for fastboot in Android SDK's platform-tools?

I know that running fastboot on its own gives a quick help for the different commands, but I'd like to know about details such as:


update: What does update.zip need to look like
flashall: Where do the flash boot + recovery + system come from, what format, etc.
boot: What is the format of &lt;kernel&gt; and what is the &lt;ramdisk&gt; option
flash:raw boot: What is the difference to boot and what is it used for


I am surprised that in the Android Developer's Tools Help there is documentation for adb but not fastboot.
Fastboot commandline utilisation as per eLinux.org is shown below.   

$ fastboot -h
usage: fastboot [ &lt;option&gt; ] &lt;command&gt;

commands:
  update &lt;filename&gt;                        reflash device from update.zip
  flashall                                 flash boot + recovery + system
  flash &lt;partition&gt; [ &lt;filename&gt; ]         write a file to a flash partition
  erase &lt;partition&gt;                        erase a flash partition
  getvar &lt;variable&gt;                        display a bootloader variable
  boot &lt;kernel&gt; [ &lt;ramdisk&gt; ]              download and boot kernel
  flash:raw boot &lt;kernel&gt; [ &lt;ramdisk&gt; ]    create bootimage and flash it
  devices                                  list all connected devices
  reboot                                   reboot device normally
  reboot-bootloader                        reboot device into bootloader

options:
  -w                                       erase userdata and cache
  -s &lt;serial number&gt;                       specify device serial number
  -p &lt;product&gt;                             specify product name
  -c &lt;cmdline&gt;                             override kernel commandline
  -i &lt;vendor id&gt;                           specify a custom USB vendor id



  update: What does update.zip need to look like


In general, fastboot flashes only .img files. 

The update.zip generally consists of .img files which will be flashed to the particular partition. A typical  update.zip file to flash via fastboot will have following files and more

boot.img
recovery.img
system.img
userdata.img
radio.img
etc...



  flashall: Where do the flash boot + recovery + system come from, what
  format, etc.


flashall will flash the system.img, boot.img &amp; recovery.img in the current/PATH folder. These images can be obtained from the update.zip mentioned above.


  boot: What is the format of &lt;kernel&gt; and what is the &lt;ramdisk&gt; option


In fastboot boot, the &lt;kernel&gt; format is an .img file. I am not sure of the &lt;ramdisk&gt; option. My guess would be to boot a kernel with a modified ramdisk without altering the built kernel (I am not a developer, sorry).

This is what I have learnt fiddling with Nexus phones. Others can correct any obvious errors in the write up.