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This is an addition to my work for vanilla NS expression parsing. It contains few tweaks regarding binding contexts.

What is the current behavior?

1. Expression parser cannot parse indentifiers that belong to global.
2. Converter callbacks use object they are declared into as a context.

What is the new behavior?

1. Expression parser will now check if an identifier belongs to global.
2. Converter callbacks will have current binding context or the instance they were called from as function context just like the old way.

Hello World app sample with an example of supporting global:

<Page xmlns="http://schemas.nativescript.org/tns.xsd" navigatingTo="navigatingTo">
   <ActionBar title="My App" icon="" />

    <StackLayout class="p-20">
        <Label text="Tap the button" class="h1 text-center" />
        <Button text="TAP" tap="{{ onTap }}" class="-primary" />
        <Label text="{{ message }}" class="h2 text-center" textWrap="true" />
        <!-- Use of `Math` here -->
        <Label text="{{ Math.abs(_counter * -1) }}" class="h2 text-center" textWrap="true" />
    </StackLayout>
</Page>