<?php
include("sample_utils.php");                               // provides some utils and using mk
 
$swfFN = "btarea.swf";                                     // swf file name to ouput
 
$shape1 = new MKshape_container();                         // a shape ...
$shape1->add_fillStyle_solid();                            // ... with default black color
$shape1->add_rect();                                       // ... and a 100x100 default rect
$shapeTD1 = $shape1->update_tagData();                     // get tag data
 
$button1 = new MKbutton_container("", 2);                  // a button
$buttonTD1 = $button1->build_button_state($shape1, "hit"); // with only "hit" state
$buttonPB1 = $button1->update_place_tagData();             // place tag data
 
$swf = new MKswf($swfFN);                                  // the swf to generate
$swf->set_swfDir(SERVER_MKTMP);                            // set output directory
$swf->add_tagData($shapeTD1);                              // start to populate
$swf->add_tagData($buttonTD1);                             // ...
$swf->add_tagData($buttonPB1);                             // ...
$swf->swf_output();
 
$swfHeader = $swf->fetch_assoc();                          // prepare to publish to the browser
 
$str = "<div style=\"width:600; height:500; background-color:#EEEEEE; text-align:center\"><br />";
$str .= render_swf_box($swfHeader, $imgDir, false);
$str .= "<br/><strong>" .$swfFN ." created in :<br />" .SERVER_MKTMP ."</strong>";
$str .= "<br/>hit area is in the top left until 100,100</div>";
echo show_content($str, basename(__FILE__));
?> 

building "hit area" button is simple. All you have to do is define a shape drawn with desired form and the use call build_button_state method for MKbutton_container.
buttons in mk can be stored as linkage symbols in the same way of movieclips, sounds and fonts. E.g. you can store a 100x100px (default shape rectangle) and use it at run-time playing with its _xscale and _yscale to create smaller or larger transparent hit areas.