tab( 'Boo!', function(){alert('Yikes!');}, 1, 'red', 'pink', 'black' );

function tab( html, action, corner, fg, bg, border )
{
  var id = 'tab-' + html.replace( /\W/g, '' );
  border = border || 'black';
  fg = fg || border;
  bg = bg || 'white';

  function addStyles( node, styles )
  {
    for( var i in styles )
      node.style[i] = styles[i];
  };

  function borderize( node )
  {
    var container = document.createElement( 'div' );
    var div = document.createElement( 'div' ), i;
    var hor = corner&1 ? 'Right' : 'Left', ch = corner&1 ? 'Left' : 'Right';
    var ver = corner&2 ? 'Bottom' : 'Top', cv = corner&2 ? 'Top' : 'Bottom';
    var styles = { zIndex:'99999', position:'fixed', width:'auto',
		   padding:'0px', border:'0px' };
    styles[hor.toLowerCase()] = styles[ver.toLowerCase()] = '0px';
    styles[ch.toLowerCase()] = 'auto';
    var common = { border:'0px solid '+border, overflow:'hidden',
  		 display:'block', backgroundColor:bg, fontSize:'1px',
  		 padding:'0px', width:'auto' },
        divstyle = { border:'0px solid '+border, background:bg,
		     width:'auto', paddingLeft:'5px', paddingRight:'5px',
		     cursor:'pointer' },
        round = [{height:'2px'},{height:'1px'},{height:'1px'},{height:'0px'}];
    for( i=0; i<round.length; i++ )
    {
      round[i]['margin'+ch] = [1,2,3,5][i] + 'px';
      round[i]['border'+ch+'Width'] = [1,1,2,0][i] + 'px';
    }
    round[3]['border'+ver+'Width'] = '1px';
    divstyle['padding'+cv+'Width'] = '1px';
    divstyle['padding'+ver+'Width'] = '2px';
    divstyle['border'+ch+'Width'] = '1px';

    div.appendChild( node );
    addStyles( div, divstyle );
    addStyles( container, styles );
    if( ver == 'Top' )
      container.appendChild( div );
    for( var i=0; i<round.length; i++ )
    {
      node = document.createElement( 'div' );
      addStyles( node, common );
      addStyles( node, round[ver=='Top' ? i : 3-i] );
      container.appendChild( node );
    }
    if( ver != 'Top' )
      container.appendChild( div );
    return container;
  };

  function addTab( id )
  {
    var a = document.getElementById( id );
    var style = { textDecoration:'none', background:bg, color:fg };
    if( a )
      return; // done that
    else
    {
      a = document.createElement( 'a' );
      addStyles( a, style );
      a.id = id;
      a.addEventListener( 'click', action, false );
      var div = borderize( a );
      document.body.appendChild( div );
    }
    a.innerHTML = html;
  };

  addTab( id );
  return id;
}