Clever templating use cases can optimize memory usage by sharing template content.

e.g.

<template iterate="foo">
  <span>{{ Person }}</span>
  <template iterate="stuffInPocket">
     <span>{{ whatsInPocket }}</span>
  </template>
</template>

---

The templating library is likely to stamp out multiple copies of 

  <span>{{ Person }}</span>
  <template iterate="stuffInPocket">
     <span>{{ whatsInPocket }}</span>
  </template>

maybe there's some way that each instance doesn't have to have a generated <template> element that contains exactly the same 
  
  <span>{{ whatsInPocket }}</span>

content docFrag

---

we could make content read-write, but then badness might occur if the content is assigned a docFrag owned by the outer document.