Access parent variable from nested block in JsRender

How can I access props's key from a nested for?

{{props object.items}}
    {{:key}}
    {{for prop.other_items}}
        {{:key}} //here I want to print the key from props

I've tried:

{{:key}}
{{:#key}}
{{:#parent.key}}
{{:#parent.parent.key}}
{{:~root.key}}

Here are three alternative ways:

Provide the key as a contextual template variable, so it is available in the {{for}} block:

{{props object.items}}
    {{:key}}
    {{for prop.other_items ~outerKey=key}}
        Outer key: {{:~outerKey}}
   {{/for}}
{{/props}}

Provide the data item of the {{props}} block (the {key: ..., prop: ...} object) as a contextual template variable, so it is available in the {{for}} block:

{{props object.items itemVar="~outerProp"}}
    {{:key}}
    {{for prop.other_items}}
        Outer key: {{:~outerProp.key}}
    {{/for}}
{{/props}}

Step up through the parent views (array view, then props item view) and get the data item (the {key: ..., prop: ...} object):

{{props object.items}}
    {{:key}}
    {{for prop.other_items}}
        Outer key: {{:#parent.parent.data.key}}
    {{/for}}
{{/props}}

And here is a link to a related reply to a previous question from Matias: https://stackoverflow.com/a/31362057/1054484