I\'ve got a handlebar template that loads a partial for a sub-element.
I would need to access a variable from the parent context in the calling template, from within
To get specifically the parent of the partial (where you may be several partials deep) then follow the other answers like SeanWM.
If you know that the parent is the main template then you can use @root which resolves to the top-most context no matter how deep you are.
e.g. {{@root.rootObject.rootProperty}}
It is a pity that ../../.. does not go up past a partial.