[JavaScript] Metody setSelectionRange + scrollTop Opcje

[amii]

Generalnie to chodzi mi o zrozumienie co robi ta funkcja tag poniżej. Nie kapuje co robią metody setSelectionRange + document.selection.createRange().text + scrollTop, wujek Google nie za bardzo pomaga tym razem. Dodatkowo co to za dziwna składnia i czemu to służy -> start = '[func]'+url+':|:'; lub start = '[break]';

[JAVASCRIPT] pobierz, plaintext 
function tag(tag) {
		var src = document.getElementById('txt');
		var start, end, url, alt, title='';
		switch(tag) {
			case 'underline': 
				start = '<span class="underline">'; 
				end = '<\/span>'; 
				break;
			case 'intro': 
				start = '[break]'; 
				end = '\n'; 
				break;
			// function use
			case 'func':// adding function insertion
				// function name no brackets
				url = prompt("<?php echo l('js_func1'); ?>", '');
				//params, seperated by comma.
				title = prompt("<?php echo l('js_func2'); ?>", "");
				if (url != null) {
					start = '[func]'+url+':|:'; 
					end = '[\/func]';
				} else {
					start = ''; 
					end = ''; 
					title = '';
				}
				break;
			// function use end
			case 'include':
				url = prompt("<?php echo l('js_file'); ?>", '');
				start = url !=null ? '[include]'+url+'[\/include]' : '';
				end = '';
				break;
			case 'br': 
				start = ''; 
				end = '<br \/>\n'; 
				break;
			case 'img':
				url = prompt("<?php echo l('js_image1'); ?>", '');
				alt = prompt("<?php echo l('js_image2'); ?>", '');
				start = url != null ? '<img src="'+url+'" alt="'+alt+'" \/>' : '';
				end = '';
				break;
			case 'link':
				url = prompt("<?php echo l('js_link1'); ?>", '');
				title = prompt("<?php echo l('js_link2'); ?>", '');
				if (url != null) {
					start = '<a href="'+url+'" title="'+title+'">'; 
					end = '<\/a>';
				} else {
					start = '';
					end = ''; 
					title = '';
				}
				break;
			default: 
				start = '<'+tag+'>'; 
				end = '<\/'+tag+'>\n';
		}
		if (!src.setSelectionRange) {
         	var selected = document.selection.createRange().text;
         	src.focus();
         	if (selected.length <= 0) {
         		var codetext = start + title + end;
         	} else {
         		var codetext = start + selected + end;
         	}
         	document.selection.createRange().text = codetext;
      	} else {
        	var h = src.scrollTop;
         	var pretext = src.value.substring(0, src.selectionStart);
         	var codetext = start + src.value.substring(src.selectionStart, src.selectionEnd) + end;
         	var posttext = src.value.substring(src.selectionEnd, src.value.length);
         	if (codetext == start + end) {
         		codetext = start + title + end;
         	}
         	src.value = pretext + codetext + posttext;
         	document.getElementById("txt").scrollTop = h;
         	src.selectionStart=pretext.length;
         	src.selectionEnd=pretext.length+codetext.length;
         	src.focus();
		}
	}
[JAVASCRIPT] pobierz, plaintext 

Przykładowe zastosowanie:

[PHP] pobierz, plaintext 
function buttons(){
       echo '<div class="clearer"></div>
    <p>'.l('formatting').':
    <br class="clearer" />';
       $formatting = array(
        'strong' => '',
        'em' => 'key',
        'underline' => 'key',
        'del' => 'key',
        'p' => '',
        'br' => ''
    );
       foreach ($formatting as $key => $var) {
          $css = $var == 'key' ? $key :'buttons';
          echo '<input type="button" name="'.$key.'" title="'.l($key).'" class="'.$css.'" onclick="tag(\''.$key.'\')" value="'.
        l($key.'_value').'" />';
    }
       echo '</p><br class="clearer" /><p>'.l('insert').': <br class="clearer" />';
       $insert = array('img', 'link', 'include', 'func','intro');
       foreach ($insert as $key) {
          echo '<input type="button" name="'.$key.'" title="'.l($key).'" class="buttons" onclick="tag(\''.
        $key.'\')" value="'.l($key.'_value').'" />';
    }
       echo '<br class="clearer" /></p>';
}
	}
[PHP] pobierz, plaintext