说明
let g:auto_save = 1 " enable AutoSave on Vim startup可以看官网有解释：https://github.com/907th/vim-auto-save
let g:auto_save_events = ["InsertLeave"]
The events on which AutoSave will perform a save can be adjusted using the g:auto_save_events option. let g:
I often see in vim plugin something like these :
let g:variable
let b:variable
let l:variable
global-variable g: Global.
buffer-variable b: Local to the current buffer.
local-variable l: Local to a function.
就是给全局变量赋值。