nsIMicrosummaryGenerator Interface

 Calculate the interval until the microsummary should be updated for
 the next time, depending on the page content. If the generator doesn't
 specify an interval, null is returned.

 @param   pageContent
          the content of the page being summarized
 @returns the interval in milliseconds until the next update request

long calculateUpdateInterval(in nsIDOMNode aPageContent)

 microsummary-generator equivalence test
 generators equal if their canonical locations equal, see uri attribute.

boolean equals(in nsIMicrosummaryGenerator aOther)

 Generate a microsummary by processing the generator template
 against the page content.  If a generator doesn't need content,
 pass null as the parameter to this method.

 XXX In the future, this should support returning rich text content,
 so perhaps we should make it return a DOM node now and have the caller
 convert that to text if it doesn't support rich content.

 @param   pageContent
          the content of the page being summarized
 @returns the text result of processing the template

AString generateMicrosummary(in nsIDOMNode aPageContent)