Flex 4 documentation article named "Selecting and modifying text" lists an finite final list of components that supports the selection:

• RichEditableText
• Label (Spark only)
• TextInput (both MX and Spark)
• TextArea (both MX and Spark)
• RichTextEditor and all controls that have a TextArea as a subcomponent

   This list does not include RichText component, but luckily with a new Text Layout Framework (TLF) available starting from Flash player 10, it is quite easy to "simulate" dynamic selection of the text with some ActionScript 3 code.

   In the following example, try to drag the slider to the left and to the right to control the dynamic selection of the text of RichText component:

Code listing:

<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009" 
               xmlns:s="library://ns.adobe.com/flex/spark" 
               xmlns:mx="library://ns.adobe.com/flex/halo"
               width="200"
               height="75">
    <s:layout>
        <s:HorizontalLayout paddingLeft="25"
                            paddingTop="25"
                            paddingRight="25"/>
    </s:layout>
    <fx:Script>
        <![CDATA[            
            import flashx.textLayout.edit.EditManager;
            import flashx.textLayout.edit.SelectionState;
            import flashx.textLayout.formats.TextLayoutFormat;            
 
            protected function highlightItem(endSelectionCharIndex : int):void
            {
                var containerFormat:TextLayoutFormat = new TextLayoutFormat();                
                var paragraphFormat:TextLayoutFormat = new TextLayoutFormat();                
                var characterFormat:TextLayoutFormat = new TextLayoutFormat();
 
                characterFormat = _selectedTextFormat;
 
                var selectionState : SelectionState = new SelectionState(rt.textFlow, 0, endSelectionCharIndex, _selectedTextFormat);                
 
                // apply format to the selection
                _textEditManager.applyFormat(
                    characterFormat, 
                    paragraphFormat, 
                    containerFormat, 
                    selectionState);                                
 
                characterFormat = _notSelectedTextFormat;                
 
                // apply format to the rest of the text
                var notSelectionState : SelectionState = new SelectionState(rt.textFlow, endSelectionCharIndex, rt.text.length, _notSelectedTextFormat);                
                _textEditManager.applyFormat(
                    characterFormat, paragraphFormat, containerFormat, notSelectionState);
            }
 
 
            protected function onRichTextCreationComplete():void
            {
                _textEditManager = new EditManager();
                rt.textFlow.interactionManager = _textEditManager;
 
                _selectedTextFormat = new TextLayoutFormat();
                _selectedTextFormat.backgroundColor = 0xFF99CC;
                _selectedTextFormat.color = 0x000000;
 
                _notSelectedTextFormat = new TextLayoutFormat();
                _notSelectedTextFormat.backgroundColor = 0xFFFFFF;
                _notSelectedTextFormat.color = 0x000000;
            }
 
            private var _textEditManager : EditManager;
 
            private var _selectedTextFormat : TextLayoutFormat;
 
            private var _notSelectedTextFormat : TextLayoutFormat;            
 
        ]]>
    </fx:Script>                   
    <s:RichText id="rt" text="Sample text" 
                creationComplete="onRichTextCreationComplete()"/>
    <s:HSlider id="slider" 
              minimum="0" 
              maximum="10" 
              change="highlightItem(slider.value)">        
    </s:HSlider>        
</s:Application>

The issue:

I was stumbled upon once ago when I loaded my external SWF file authored by the Flash IDE by the help of component and suddenly (?) every content object that was originally placed outside of the Stage inside the Flash IDE became visible in my Flex 2 based web application outside of the boundaries after loading sequence for my external SWF file was over (the file is Flash8 based, AVM1 if this matters).

The corresponding task in Adobe JIRA bug-database:
http://bugs.adobe.com/jira/browse/SDK-14590

I currently fight this issue by applying the mask over the content that is loaded by the component, see the code below, may be you can find it helpful too:

[sourcecode language="xml"]
<?xml version="1.0" encoding="utf-8"?>
<mx:VBox xmlns:mx="http://www.adobe.com/2006/mxml"
resize="applyMask()" >

<mx:Script>
<![CDATA[
private function applyMask() : void {
if (swf != null &&
swf.content != null &&
swf.content.loaderInfo.width > 0 &&
swf.content.loaderInfo.height > 0) {
var scaleRatioX : Number = swf.content.loaderInfo.width /
this.width;
var scaleRatioY : Number = swf.content.loaderInfo.height /
(this.height - this.controlBar.height);
var scaleRatio : Number = Math.max(scaleRatioX, scaleRatioY);

swf.width = swf.content.loaderInfo.width > 0 ?
Math.round(swf.content.loaderInfo.width / scaleRatio) : 100;
swf.height = swf.content.loaderInfo.height > 0 ?
Math.round(swf.content.loaderInfo.height / scaleRatio) : 100;

var s : Shape = new Shape();
s.graphics.beginFill(0xFFFFFF);
s.graphics.drawRect(0, 0, swf.width, swf.height);
s.graphics.endFill();
swf.addChild(s);
s.visible = false;
swf.mask = s;
}
}
]]>
</mx:Script>
<mx:SWFLoader id="swf"
complete="applyMask()"
source="navigation.swf"/>
</mx:VBox>
[/sourcecode]

The steps I underwent:

1. I had installed Flex Builder 3 beta 2 (FB 3 beta 2) as a plugin on my Eclipse 3.2
2. Opened my Flex SWF Library projects inside of Flex Builder 3 beta 2
3. Selected Flex 3 M3 (Beta 2) SDK at the dialog (default value)
4. Flex Buidler 2 had given me the following error in my log file: (full error info skipped for the sake of text clarity)

java.lang.IllegalArgumentException: Attempted to beginRule: P/FlexLibrary, does not match outer scope rule: P/as3corelib
at com.adobe.flexbuilder.project.actionscript.internal.FlexProjectPreferences.setUpgradeFlexSDK
(FlexProjectPreferences.java:147)
at com.adobe.flexbuilder.project.actionscript.internal.ActionScriptProjectSettings$2.runInUIThread
(ActionScriptProjectSettings.java:285)

5. Nevertheless of the received error, I was able to compile ALL my Flex 2 based projects that relies on my Flex SWC Library projects in FB 3 Beta 2
6. Then I had reopened my plain Flex projects inside Flex Builder 2 again, because at the company we are using currently Flex Builder 2 for the production.
7. But Flex Builder 2 constantly had failed to recompile all Flex SWC Library projects that were previously opened at least once at FB 3 beta2.

My resolution to this issue was to delete manually a config file created by FB 3 beta 2 and located at each Flex SWC library project folder at the following path:

c:\workspace\\.settings\com.adobe.flexbuilder.project.prefs

Mine Flex 2 authored SWF is 19 levels deep in its full glory:

[sourcecode language="actionScript3"]_level0.index0.VBox5.GradientBox25.indexViewStack.
mainPage.contentPane.mainViewStack.customerViewStack.
presentationViewer.swf.FlexLoader396.instance458.sfiViewer.
bank.foreground.sa04d14eaa39b3fd.content.clip[/sourcecode]

    Sometimes the look of <mx:LinkButton> look is not enough to satisfy the designer's requirement to display hyperlinks inside you Flex 2 application in a way we got used to see them in HTML world, e.g. to display hyperlinks inside Flex 2 in a plain text.

Luckily Flash 9 supports pseudo CSS style selectors like a:hover, a:link, a:active. Let's use this fact to our advantage!

Source MXML code of the example project:

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<?xml version="1.0" encoding="utf-8"?>
<mx:Application
    xmlns:mx="http://www.adobe.com/2006/mxml"
    layout="vertical"
    xmlns:text="jabbypanda.controls.*"
    width="100%" height="100%"
    horizontalAlign="center"
    backgroundGradientColors="[#000000, #282828]" backgroundColor="#282828"
    verticalAlign="middle" viewSourceURL="srcview/index.html">
 <mx:Script>
     <![CDATA[
         import jabbypanda.controls.HyperLink;
         import jabbypanda.controls.events.HyperlinkEvent;
 
        private function onLinkClick(evt : HyperlinkEvent) : void {
            // here you can invoke loading of external web-page if you want    via URLRequest
             var hControl : HyperLink = HyperLink(evt.target);
            txtDataUrl.text = "You just had clicked '" + hControl.linkText + "'";
            txtDataUrl.visible = true;
          }
 
          private function changeStyle() : void {
              hLink.setStyle("colorLink", 0xFFFF00);
              hLink.setStyle("colorHover", 0xFFFF00);
              txtDataUrl.visible = false;
          }
     ]]>
 </mx:Script>
 <mx:Style>
     HyperLink {
         colorLink : #FF0000;
         colorHover : #00FF00;
         colorActive : #0000FF;
     }
 
     Label {
         color : #CCCCCC;
         fontSize : 16;
     }
 
 </mx:Style>
  <text:HyperLink linkText="Click me! I am a hypertext link" id="hLink" linkClick="onLinkClick(event)"/>
  <mx:Button id="btn" label="Change the style" click="changeStyle()"/>
  <mx:Label id="txtDataUrl" visible="false"/>
</mx:Application>

See the demo below.

Example: http://jabbypanda.com/labs/hyperLink/htmlText.html
Source files: http://jabbypanda.com/labs/hyperLink/srcview/index.html

ps
I marked this component version as 0.1 because I feel there is a open room for suggestion how to correct/ extend Hyperlink component to make it more useful.

Tell me frankly, does this hyperlink component look good enough to match a view and feel of plain old <a href> tag from HTML world?

Acknowledgments

Hyperlink component example written by Tracy Spratt