Bracket Expression
    [key]
  
  Evaluates key and looks up the result in the scope.
{{[key]}}
  
  Parameters
- key 
{Literal Expression|KeyLookup Expression|Call Expression|Helper Expression}:A Literal, KeyLookup, Call, or Helper expression to evaluate and look up the result in the scope.
 
    CALL_EXPRESSION[key]
  
  Evaluates key and looks up the result in the return value of CALL_EXPRESSION.
{{method()[key]}}
  
  Parameters
- CALL_EXPRESSION 
{Call Expression|Helper Expression|KeyLookup Expression}:A Call, Helper, or KeyLookup expression that may or may not return a value.
 - key 
{Literal Expression|KeyLookup Expression|Call Expression|Helper Expression}:A Literal, KeyLookup, Call, or Helper expression to evaluate and look up the result in the result of
CALL_EXPRESSION. 
Use
A bracket expression can be used to look up a dynamic property in the scope. This looks like:
Template:
    <h1>{{[key]}}</h1>
Data:
    {
        key: "name",
        name: "Kevin"
    }
Result:
    <h1>Kevin</h1>
This can be useful for looking up values using keys containing non-alphabetic characters:
Template:
    <h1>{{["person:name"]}}</h1>
Data:
    {
        "person:name": "Kevin"
    }
Result:
    <h1>Kevin</h1>
Bracket expressions can also be used to look up a value in the result of another expression:
Template:
{{getPerson()[key]}}
Data:
    {
        key: "name",
        getPerson: function() {
            return {
                name: "Kevin"
            };
        }
    }
Result:
    <h1>Kevin</h1>