[Vala] What is (instance_pos = -1) in vala

[Vishal Pawale <vishalpawale123 gmail com>]

Hi guys,

I am newbie to vala programming language.So I was going through sample code
and encountered "[CCode (instance_pos = -1)]".

I know about what CCode does but what "instance_pos" is used for?

Also this is OT question but if you guys can help me with this ==> I am
using Anjuta IDE for programming.I am not able to use intellisense in it so
do I need to enable it and if so how to do that?