%index

When looping over an array, can-define/list/list, or can-list, you an use %index to write out the index of each property:

{{#each(tasks)}}
  <li>{{%index}} {{name}}</li>
{{/each}}

Indexes start at 0. If you want to start at 1, you can create a helper like:

stache.registerHelper('%indexNum', function(options) {
  return options.scope.get("%index") + 1;
});

And use it like:

{{#each(task)}}
  <li>{{%indexNum}} {{name}}</li>
{{/each}}

%key

Like %index, but provides the key value when looping through an object:

{{#each(style)}}
   {{%key}}: {{this}}
{{/each}}

%element

In an event binding, %element references the DOM element the event happened on:

<input ($click)="doSomething(%element.value)"/>

%event

In an event binding, %event references the dispatched event object:

<input ($click)="doSomething(%event)"/>

%viewModel

In an event binding, %viewModel references the view model of the current element:

<my-component (closed)="doSomething(%viewModel)"/>

%arguments

In an event binding, %arguments references the arguments passed when the event was dispatched/triggered.

<input ($click)="doSomething(%arguments)"/>