Read 
the Mishoo documentation or
visit the demo page for detailed information 
on using the calendar widget.
This plugin includes the following function to make using the calendar
easier from other TWiki plugins:
 renderForEdit 
TWiki::Plugins::DatePickerPlugin::renderForEdit( $name, $value, $format [, \%options] ) -> $html
This is the simplest way to use calendars from a plugin. 
-  $nameis the name of the CGI parameter for the calendar     (it should be unique),
-  $valueis the current value of the parameter (may be undef)
-  $formatis the format to use (optional; the default is set     inconfigure). The HTML returned will display a date field     and a drop-down calendar.
-  \%optionsis an optional hash containing base options for     the textfield.
Notes:
-  The CSS and Javascript are added if needed, e.g. the addToHEAD()function does not need to be called.
-  No output is shown if $nameis empty or undef, but the CSS and     Javascript are loaded if needed. This can be used to preload the     CSS and Javascript with a parameterless%DATEPICKER{}%variable.
Example:
use TWiki::Plugins::DatePickerPlugin;
...
my $fromDate = TWiki::Plugins::DatePickerPlugin::renderForEdit(
   'from', '2012-12-31');
my $toDate = TWiki::Plugins::DatePickerPlugin::renderForEdit(
   'to', undef, '%Y');
 addToHEAD 
TWiki::Plugins::DatePickerPlugin::addToHEAD( $setup )
This function will automatically add the headers for the calendar to the page
being rendered. It's intended for use when you want more control over the
formatting of your calendars than 
renderForEdit affords. 
$setup is the name
of the calendar setup module; it can either be omitted, in which case the method
described in the Mishoo documentation can be used to create calendars, or it
can be 
'twiki', in which case a Javascript helper function called
'showCalendar' is added that simplifies using calendars to set a value in a
text field. For example, say we wanted to display the date with the calendar
icon 
before the text field, using the format 
%Y %b %e
use TWiki::Plugins::DatePickerPlugin;
...
sub commonTagsHandler {
  ....
  # Add styles and javascript for the date picker & enable 'showCalendar'
  TWiki::Plugins::DatePickerPlugin::addToHEAD( 'twiki' );
  my $cal = CGI::image_button(
      -name => 'img_datefield',
      -onclick =>
       "return showCalendar('id_datefield','%Y %b %e')",
      -src=> TWiki::Func::getPubUrlPath() . '/' .
             TWiki::Func::getTwikiWebname() .
             '/DatePickerPlugin/img.gif',
      -alt => 'Calendar',
      -align => 'middle' )
    . CGI::textfield(
      { name => 'date', id => "id_datefield" });
  ....
}
The first parameter to 
showCalendar is the id of the textfield, and the 
second parameter is the date format. Default format is 
'%Y-%m-%d'.
The 
addToHEAD function can be called from 
commonTagsHandler for adding
the header to all pages, or from 
beforeEditHandler just for edit pages etc.