[whatwg] "first script" and impersonating other pages - pushState(url)

[Mike Wilson]

I'm currently wrapping my head around the notion of
"first script" in the spec [1]. It's description is
a bit terse and the subject seems non-trivial, so 
maybe the text could be fleshed out some?

Section 6.1.5 "Groupings of browsing contexts" says:
| Each unit of related similar-origin browsing 
| contexts can have a first script which is used to 
| obtain, amongst other things, the script's base 
| URL to resolve relative URLs used in scripts 
| running in that unit of related similar-origin 
| browsing contexts. Initially, there is no first 
| script.

Ok, so a *unit of related similar-origin browsing 
contexts* has one shared first script.

Does this implicitly say that this set of browsing
contexts should never execute script in parallel?
(= mutually exclusive code execution, so one 
hang will hang them all)

Section 6.5.3.2 "Calling scripts" says:
| When a user agent is to jump to a code entry-point 
| for a script, for example to invoke an event 
| listener defined in that script, the user agent 
| must run the following steps:
| [...]
| 2. Set the first script to be the script being 
|    invoked. 

Example:

  /pages/page1.html:
    <script src="/scripts/script1.js">
*1  <button onclick="func1();">

  /scripts/script1.js:
    function func1() { ... }
*2  func1();

What is regarded as *first script* in these two 
calls to func1() ?
*1: the implicitly generated event handler wrapper 
    in /pages/page1.html ?
*2: /scripts/script1.js

Section 6.10.2 "The History interface" says:
| [...]
| pushState(data, title, url)
| [...]
| 2.1 Resolve the value of the third argument, 
|     relative to the first script's base URL.
| [...]
| 5   If the third argument is present, set the 
|     document's current address to the absolute URL 
|     that was found earlier in this algorithm.

Ok, by calling pushState() with an URL I can make 
the address bar show another URL than my document is
loaded from.

Imagine that I want my loaded page:
  /pages/section1/thing1
be able to impersonate:
  /pages/section2/thing2
how do you envision this to be structured? 

Something like this? :

  /pages/section1/thing1:
    <script src="/pages/script.js">
    <button onclick="impersonate();">

  /pages/script.js:
    function impersonate() {
      ...pushState(..., "/pages/section2/thing2");
    }

Best regards
Mike Wilson

[1] http://dev.w3.org/html5/spec/Overview.html
(btw, the latest WD link gives a 404:
http://www.w3.org/TR/2009/WD-html5-20090825/)