If you write script that has a lot String content mixed with variables, I'm sure you're doing a lot of heavy concatenation.
Building string combos with quotes and apostrophes sprinkled all over a script gets confusing. The way I like to keep this confusion to a minimum is to write my static markup separately. This allows me to make sure it shows up as intended. Then I concatenate my variables in all the places that need to have dynamic content.

Taking static markup or script and wrapping quotes around every line is a chore so I made this Concatenation Tool to help with that.

Currently I've only made this support languages I'm using mostly. If I have to use a new language I'd just add it in.

Below are some basic use case examples of where a concatenation tool can be useful.

JavaScript
Concatenating a content to add to a Jquery UI Dialog.
In this example I purposely used he "text()" method to show the XML content instead of "html()".

    <script type="text/javascript">
                $(document).ready(function(){
                var ns = "";
                ns += "<LIBRARY>";
                ns += "    <BOOK>";
                ns += "        <TITLE id=\"2356\">Charlotte's Web</TITLE>";
                ns += "        <AUTHOR>E. B. White</AUTHOR>";
                ns += "        <FAMOUS_SAYING>\"Always be on the lookout for the presence of wonder.\"</FAMOUS_SAYING>";
                ns += "    </BOOK>";
                ns += "    <BOOK>";
                ns += "        <TITLE id=\"95\">Scuffy the Tugboat</TITLE>";
                ns += "        <AUTHOR>Gertrude Crampton</AUTHOR>";
                ns += "        <FAMOUS_SAYING>\"Toot, tooot!\" cried the frightened tugboat.</FAMOUS_SAYING>";
                ns += "    </BOOK>";
                ns += "</LIBRARY>";
                $("#myDialog").dialog({width:400, height:400});
                $("#myDialog p").text(ns);
                });
    </script>

Python
Concatenating with qoutes

ns = ""
ns += "<LIBRARY>"
ns += "    <BOOK>"
ns += "        <TITLE id=\"2356\">Charlotte's Web</TITLE>"
ns += "        <AUTHOR>E. B. White</AUTHOR>"
ns += "        <FAMOUS_SAYING>\"Always be on the lookout for the presence of wonder.\"</FAMOUS_SAYING>"
ns += "    </BOOK>"
ns += "    <BOOK>"
ns += "        <TITLE id=\"95\">Scuffy the Tugboat</TITLE>"
ns += "        <AUTHOR>Gertrude Crampton</AUTHOR>"
ns += "        <FAMOUS_SAYING>\"Toot, tooot!\" cried the frightened tugboat.</FAMOUS_SAYING>"
ns += "    </BOOK>"
ns += "</LIBRARY>"
print(ns)

Python concatenation with triple quotes to preserve the carriage returns

ns="""<LIBRARY>
    <BOOK>
        <TITLE id="2356">Charlotte's Web</TITLE>
        <AUTHOR>E. B. White</AUTHOR>
        <FAMOUS_SAYING>"Always be on the lookout for the presence of wonder."</FAMOUS_SAYING>
    </BOOK>
    <BOOK>
        <TITLE id="95">Scuffy the Tugboat</TITLE>
        <AUTHOR>Gertrude Crampton</AUTHOR>
        <FAMOUS_SAYING>"Toot, tooot!" cried the frightened tugboat.</FAMOUS_SAYING>
    </BOOK>
</LIBRARY>"""
print(ns)

Concatenation with regular quotes

Concatenation of blocks of text with triple quotes

JSFL
Concatenating a XUL markup string for building Flash IDE Panel with JSFL.

if(fl.documents.length == 0){
	fl.createDocument("timeline");
}
//------------------------------------------------------------
//An existing folder for the panel's source to be written to.
//------------------------------------------------------------
var appFolderName="jsflUI_sample";
var date=new Date();
function writePanelSource()
{
	var code = '';
	code += '<overlay>';
	code += '	<dialog id="app" title="Sample UI">';
	code += '		<hbox>';
	code += '			<spacer/>';
	code += '			<button id="b0" label="Button"/>';
	code += '		</hbox>';
	code += '		<separator/>';
	code += '		<vbox>';
	code += '			<label control="f0" value="Field 1" align="left"/>';
	code += '			<textbox id="f0" size="50" value="'+date.toString()+'"/>';
	code += '			<label control="f1" value="Field 2:" align="left"/>';
	code += '			<textbox id="f1" size="50" value=""/>';
	code += '		</vbox>';
	code += '		<checkbox id="cb0" label="Checkbox 1" checked="false" />';
	code += '		<checkbox id="cb1" label="Checkbox 2" checked="false" />';
	code += '	</dialog>';
	code += '</overlay>';
	FLfile.write(fl.configURI + "Commands/"+appFolderName+"/panelsource.xml", code);
	return code;
}

//----------------------------------------------------------------
//Writes the markup to "appFolderName" of Flash's "Commands folder
//----------------------------------------------------------------
writePanelSource();

//-------------------------------
//Open the Panel in Flash's IDE
//-------------------------------
fl.getDocumentDOM().xmlPanel(fl.configURI + "Commands/"+appFolderName+"/panelsource.xml");

Panel UI dialog from JSFL

SharePoint
Concatenating CAML querys.

function getListData()
{
	var clientContext = new SP.ClientContext.get_current();
	var web = clientContext.get_web();
	var userInfoList = web.get_lists().getByTitle('user_list')
	var camlQuery = new SP.CamlQuery();
	var caml = '';
	caml += '<View>';
	caml += '	<Query>';
	caml += '		<OrderBy>';
	caml += '			<FieldRef Name="Title" Ascending="False" />';
	caml += '		</OrderBy>';
	caml += '	</Query>';
	caml += '</View>';
	camlQuery.set_viewXml(caml);
	collListItem = userInfoList.getItems(camlQuery);
	clientContext.load(collListItem);
	var onQuerySucceeded=function(sender, args)
	{
		var oitem;
		var s='';
		var n=0;
		var len=collListItem.get_count();
		var results=[];
		while(n < len)
		{
			oitem = collListItem.itemAt(n);
			s+="Title:"+oitem.get_item("Title")+"<br></br>";
			n++;
		}
		$("#output").append(s);
	}
	var onQueryFailed=function(sender, args)
	{
		alert("Failed getting data.")
	}
	clientContext.executeQueryAsync
        (
        Function.createDelegate(this, onQuerySucceeded),
        Function.createDelegate(this, onQueryFailed)
        );
}

Output of Title column from a SharePoint 2010 list.

In the example below I was trying to add a new PAGE node to the existing "PAGE" XMLList....

Before when I used "appendChild". Error!
Even if my XMLList had one child, it would not be the result I wanted.

 
var doc:XML=
<BOOK>
	<PAGE />
	<PAGE />
	<PAGE />
</BOOK>;
 
trace("\nOriginal...");
trace(doc.toXMLString());
doc.PAGE.appendChild(<PAGE />);
trace("\nChanges...");
trace(doc.toXMLString());
 
\\Trace Output:
Original...
<BOOK>
  <PAGE/>
  <PAGE/>
  <PAGE/>
</BOOK>
TypeError: Error #1086: The appendChild method only works on lists containing one item.
	at XMLList/http://adobe.com/AS3/2006/builtin::appendChild()
	at Untitled_fla::MainTimeline/Untitled_fla::frame1()
 

Using the compound assignment operator "+=" gives the result I was looking for. The new PAGE node is added to the XMLList.

 
var doc:XML=
<BOOK>
	<PAGE />
	<PAGE />
	<PAGE />
</BOOK>;
 
trace("\nOriginal...");
trace(doc.toXMLString());
doc.PAGE+=<PAGE />; //doc.PAGE=doc.PAGE+<PAGE />; works just as well.
trace("\nChanges...");
trace(doc.toXMLString());
 
\\Trace Output:
Original...
<BOOK>
  <PAGE/>
  <PAGE/>
  <PAGE/>
</BOOK>
 
Changes...
<BOOK>
  <PAGE/>
  <PAGE/>
  <PAGE/>
  <PAGE/>
</BOOK>
 

In the Flex framework, there is ObjectUtil.getClassInfo().properties, but I feel is more useful to just use the XML returned from the describeType method. I like using decribeType for both plain AS3 or when using the Flex framework because its accessible in both.
Since the return of describeType is XML I have more options with E4X filtering/Regular Expressions, than using getClassInfo(). With describeType I can get info on methods as well but to keep things simple I'm only talking about accessor properties in this post. Using the "listProperties" function, I am listing the properties between 3 different classes. This is a function I wrote to show how you can make your own way to use the XML of decribeType.

In the example SWF below, there are 3 classes under inspection. The Helicopter class is a custom class extending Sprite. By setting the parameters of listProperties you can list the properties of Helicopter, or all of the properties it has by being subclassed from Sprite. The other classes are a TextField and a Sprite class. Changing the options lists a different set of properties based on type of Class of properties listed and what class its properties are declared by.

 
package
{
	import flash.display.Sprite;
 
	public class Helicopter extends Sprite
	{
		private var _roll:Number=0;
		private var _pitch:Number=0;
		private var _yaw:Number=0;
 
		function Helicopter():void
		{
			super();
		}
		public function get roll():Number
		{
			return _roll;
		}
		public function set roll(v:Number):void
		{
			_roll=v;
 
		}
		public function get pitch():Number
		{
			return _pitch;
		}
		public function set pitch(v:Number):void
		{
			_pitch=v;
 
		}
		public function get yaw():Number
		{
			return _yaw;
		}
		public function set yaw(v:Number):void
		{
			_yaw=v;
 
		}
	}
}
 

 
/*============================================================
  obj						-The instance to return properties of.
  accessType				-Set to either "readwrite" or "readonly" to return only those kind of properties.
  excludeCommonWith			-Excludes all properties 'obj' has in common with the Class you give here.
  matchesRE					-If set listProperties will only return the property names that match the RegExp.
  declaredOnlyByObjClass	-If false, will not exclude properties declared by other classes than the givin 'obj'.  
 
  Returns and Array of all the properties of the instance.
 ============================================================*/
function listProperties(obj:Object, accessType:String="readwrite", excludeCommonWith:Class=null, matchesRE:RegExp=null, declaredOnlyByObjClass:Boolean=true):Array
{
	var a:XMLList;
	var b:Array=[];
	var c:*;
	var n:int;
	var doc:XML;
	var cname:String;
	matchesRE=matchesRE || new RegExp(".+");
	accessType=accessType || "readwrite";
	accessType=accessType.toLowerCase();
	if (!RegExp(/readwrite|readonly/i).test(accessType)) {
		accessType == "readwrite";
	}
	doc=flash.utils.describeType(obj);
	cname=doc.@name;
	if (declaredOnlyByObjClass) {
		a=doc.accessor.(@access == accessType && @declaredBy == cname && matchesRE["test"](@name));
	} else {
		a=doc.accessor.(@access == accessType && matchesRE["test"](@name));
	}
	if (excludeCommonWith != null) {
		c=new excludeCommonWith();
	}
	n=0;
	while (n < a.length())
	{
		if (c != null) {
			if (Object(c).hasOwnProperty(a[n].@name) == false) {
				b.push(a[n].@name);
			}
		} else {
			b.push(a[n].@name);
		}
		n++;
	}
	return b;
}
 

download fla

Here, the example scripts pull a list of all the nodes with the name "MEDIA".
Using Regular Expressions, you can identify each "MEDIA" node regardless of its letter case.

 
var doc:XML=
<DATA>
	<CATEGORY>
		<MEDIA>A.jpg</MEDIA>
		<MEDIA>B.jpg</MEDIA>
	</CATEGORY>
	<CATEGORY>
		<MEDIA>C.jpg</MEDIA>
	</CATEGORY>
	<CATEGORY>
		<MEDIA>D.jpg</MEDIA>
	</CATEGORY>
	<CATEGORY>
		<MEDIA>E.jpg</MEDIA>
	</CATEGORY>
</DATA>;
 
var findName:String="media";
trace(doc..*.(new RegExp(findName,"i")["test"](name())).toXMLString());
 

"Error #1069: Property lowerCase not found on QName"

 
trace(doc..*.(name().lowerCase()=="media").toXMLString());
 

Letter case must be same for this to work.

 
trace(doc..*.(name()=="MEDIA").toXMLString());
 

Used a regular expression to do case-insensitive filter
Works, letter case does not matter...but the expression is too "hardcoded".

 
trace(doc..*.(/media/i.test(name())).toXMLString());
 

Works, but compiler does not like it:
"Warning: 3594: test is not a recognized method of the dynamic class RegExp."
This is an attempt to allow variables and expressions.

 
var findName:String="media";
trace(doc..*.(new RegExp(findName,"i").test(name())).toXMLString());
 

:jumping: Works!
"[" and "]" keeps the compiler from warning when using the RegExp "test()" method.
Now letter case does not matter, and RegExp constructor allows variables or expressions.

 
var findName:String="media";
trace(doc..*.(new RegExp(findName,"i")["test"](name())).toXMLString());
 

 
<library>
	<book>
<page id="one"/>
		<worm name="Eddy" />
<page id="two"/>
<page id="three">
			<worm name="Lisa"/>
			<worm name="Pete" />
		</page>
<page id="four"/>
	</book>
</library>
 

There are some E4X operators and XML methods to help use do this when combined together:

.. Access all descendants of the XML object.
. Access a property of an Object or XML.
* Wildcard, match any part of the XML.
childIndex() Index number of an XML object relative to its parent node.
name() Name of the XML node.

Return a certain "worm" node at the index it belongs to from its XMLList.
Any nested "worm" node occurrence is also considered.

 
var doc:XML=
<library>
	<book>
<page id="one"/>
		<worm name="Eddy" />
<page id="two"/>
<page id="three">
			<worm name="Lisa"/>
			<worm name="Pete" />
		</page>
<page id="four"/>
	</book>
</library>;
 
//Pick the "worm" node at index 1.
var data:*=doc..*.worm[1];
trace(data.toXMLString());
 
/*=========================================
OUTPUT:
 
<worm name="Lisa"/>			//worm[1]
===========================================*/
 

Delete all "worm" nodes from the xml, even the nested ones.

 
var doc:XML=
<library>
	<book>
<page id="one"/>
		<worm name="Eddy" />
<page id="two"/>
<page id="three">
			<worm name="Lisa"/>
			<worm name="Pete" />
		</page>
<page id="four"/>
	</book>
</library>;
 
delete doc..*.worm;
trace(doc.toXMLString());
 
/*=========================================
OUTPUT:
All "worm" nodes are deleted.
<library>
  <book>
<page id="one"/>
<page id="two"/>
<page id="three"/>
<page id="four"/>
  </book>
</library>
===========================================*/
 

Use E4X filtering with Regular Expressions.
XML methods and Regular Expressions can be used inside parentheses to accomplish E4X filtering.

doc..*.(childIndex()==0 && /library|book/i.test(name())==false)

List all nodes that belong at a given index of their XMLList.

 
var doc:XML=
<library>
	<book>
<page id="one"/>
		<worm name="Eddy" />
<page id="two"/>
<page id="three">
			<worm name="Lisa"/>
			<worm name="Pete" />
		</page>
<page id="four"/>
	</book>
</library>;
 
//----------------------------------------------------
//Get the first node of each list whose name does not
//match the regular expression.
//----------------------------------------------------
var data:*=doc..*.(childIndex()==0 && /library|book/i.test(name())==false);
trace(data.toXMLString());
 
/*=========================================
OUTPUT:
<page id="one"/>
<worm name="Lisa"/>
===========================================*/
 

 
/*-----------------------------------
	Recursively replace nodeNames.
-------------------------------------*/
      private function findAndReplaceTagNames
      (xml:XML,find:String,replace:String):XML
      {
          if(xml.localName() == find){
              xml.setLocalName(replace);
          }
          var n:int=0;
          var c:XML;
          while(n <xml.children().length()){
              c=xml.children()[n];
              findAndReplaceTagNames(c,find,replace);
              n++;
          }
          return xml;
      }
 
/*-----------------------------------------
	Recursively replace attributes.
-------------------------------------------*/
      private function findAndReplaceAttributeNames
      (xml:XML,find:String,replace:String,in_tags_named:String=""):XML
      {
          var ok:Boolean=true;
          if(in_tags_named != "" && xml.localName() != in_tags_named){
              ok=false;
          }
          if(xml.@[find] != null && ok){
              xml.@[replace]=xml.@[find];
              delete xml.@[find];
          }
          var n:int=0;
          var c:XML;
          while(n <xml.children().length()){
              c=xml.children()[n];
              findAndReplaceAttributeNames(c,find,replace);
              n++;
          }
          return xml;
      }
 
/*---------------------------------------------
	Recursively find and remove attributes.
-----------------------------------------------*/
      private function findAndRemoveAttributeNames
      (xml:XML,find:String,in_tags_named:String=""):XML
      {
          var ok:Boolean=true;
          if(in_tags_named != "" && xml.localName() != in_tags_named){
              ok=false;
          }
          if(xml.@[find] != null && ok){
              delete xml.@[find];
          }
          var n:int=0;
          var c:XML;
          while(n <xml.children().length()){
              c=xml.children()[n];
              findAndRemoveAttributeNames(c,find);
              n++;
          }
          return xml;
      }