Xen and reorder menu item wording to make it clearer that this entry will launch Xen. Print separate messages when loading Xen and Linux.
All executable files in this directory are processed in shell expansion order. 00_*: Reserved for 00_header. 10_*: Native boot entries. 20_*: Third party apps (e.g. memtest86+). The number namespace in-between is configurable by system installer and/or administrator. For example, you can add an entry to boot another OS as 01_otheros, 11_otheros, etc, depending on the position you want it to occupy in the menu; and then adjust the default setting via /etc/default/grub.