=head1 NAME

GvaScript.protoExtensions - Extensions to prototype.js

=head1 SYNOPSIS

  Element.hasAnyClass(elem, ["class1", "class2", ...]);  
  Element.getElementsByClassNames(elem, ["class1", "class2", ...]);  

  var stop_condition = function(elem) { return elem.tagName == "SPAN"};
  Element.navigateDom(elem, "nextSibling", ["class1", "class2", ...],
                       stop_condition);

  this.options = Class.checkOptions(defaultOptions, receivedOptions);


=head1 DESCRIPTION

Some extensions to the basic abstractions supplied by
prototype.js.

=head1 METHODS

=head2 Element extensions

=head3 hasAnyClass

  if (Element.hasAnyClass(elem, ["class1", "class2", ...]) {...}  

  if (Element.hasAnyClass(elem, "class1") {...}  

Returns true if the supplied element has any of the given classes. 
For convenience, also accepts a single string instead of an array
when testing for a single class.

=head3 getElementsByClassNames

  var subElements 
     = Element.getElementsByClassNames(rootElement, ["class1", "class2", ...]);

Returns an array of children of C<rootElement> that have any
of the given class names.

=head3 navigateDom

  var wantedClasses = ["class1", "class2", ...];
  
  // which direction to navigate (could be "parentNode", etc.)
  var direction     = "nextSibling"; 

  // some criteria for stopping navigation (can be anything, here a stupid
  // example)
  var stopCondition = function(elem) {return elem.innerHTML.length > 10}

  var nextElement
    = Element.navigateDom(startElement, direction, wantedClasses,
                          stopCondition);


Walks through the DOM in the given direction, until finding an
element that has one of the given classnames, or finding a stop
condition (in which case C<null> is returned).


=head3 autoScroll

  Element.autoScroll(elem, percentage) 

Makes sure that C<elem> is visible in the central area of 
its offset parent; if not, the parent is scrolled.
C<percentage> is the ratio between the parent height and the 
margin at which scrolling must occur, i.e. if 
C<percentage = 20> (the default), then scrolling
occurs if the element is in the higher than the top 20% or 
lower than the bottom 20% of the viewport.


=head3 outerHTML

  Element.outerHTML(elem)

Returns a string representation of the DOM element,
including tags and attributes. Implemented through
the native C<outerHTML> property, if present; otherwise
constructs a string from tag name, attributes and 
innerHTML property.
   


=head2 Event extensions

=head3 detailedStop

  Event.detailedStop(event, toStop);

Browser-independent method to control fine details of
event stopping within event handlers. 
The C<toStop> argument is an object
which may contain the following properties:

=over

=item stopPropagation

if true, the event will not be passed  to further
handlers up the bubbling hierarchy.

=item preventDefault

if true, the default behaviour of the browser
for that event will be cancelled

=back

=head3 stopAll

Just a convenience object, having both properties
above set to true. So 

  Event.detailedStop(event, Event.stopAll);

is equivalent to calling prototype's C<Event.stop(event)>.


=head2 Class extensions

=head3 checkOptions

  this.options = Class.checkOptions(defaultOptions, ctorOptions)

Utility for constructor methods. The first argument is an object
containing a collection of default options (keys and values).
The second argument is a similar object, containing options
given to the constructor. 

If one of the keys in C<ctorOptions> has no corresponding
key in  C<defaultOptions>, an error is generated (because
the constructor does not expect such a key). Otherwise,
the concatenation of both objects is returned (i.e. values
in C<ctorOptions> take precedence over values in 
C<defaultOptions>).

=head2 ASSERT

  ASSERT (cond, msg);

Checks if C<cond> is true, and if not, generates an error 
with message C<msg>.