additional functionality for html-helper-mode

[ken]

Another current conversation about emacs & elisp programming got me 
thinking again....

There is some mode in emacs which can selectively and flexibly 
"collapse" and "expand" selected blocks of text; that is, make it/them 
visible to the user or not display them.  It was a long time ago, but I 
believe that was org-mode.

Would it be possible to integrate that functionality into 
html-helper-mode so that chapters could be selectively collapsed or 
expanded?  For example, I might have:

<h1>Chapter One</h1>

<p>This is a paragraph.  There would be many of these.

 </p>

<h1>Chapter Two</h1>

<p>Paragraph in Chapter II. blah blah blah

 </p>

<h1>Chapter Three</h1>

<p>More paragraphs for this chapter also.

 </p>

Then I'd want to not see the contents of chapter 2 only, like this:

<h1>Chapter One</h1>

<h1>Chapter Two</h1>

<p>Paragraph in Chapter II. blah blah blah

 </p>

<h1>Chapter Three</h1>

Of course all the text for all chapters would still be there in the 
file, just not visible in emacs.  I could still pull the file into a 
browser and see the entire thing.

I'm fairly certain this would be possible.  The question is, I guess, 
what would be the easiest way to do it?

Much thanks.