create a PlainTextExporter extends ConverterBase and implements ITextImporter, and

 

TextConverter.addFormatAt(0, "plainText", PlainTextImporter);

1. Did you create PlainTextExporter but register PlainTextImporter? I believe it must be a typo.

2. What's more, the fifth paramter of addFormatAt should not be null when you take advantage of Custom Clipboard.

/**

                     * Register a new format for import/export, at the specified location.

                     * Location can be significant for clients that have multiple

                     * choices for which format to use, such as when importing from the external clipboard.

                     * Lower numbers indicate higher priority; these converters will be tried first.

                     * The new format may support importing and/or exporting.

                     * If the format has already been added, then it will be present in multiple locations. The

                     * first one found will be used.

                     *

                     * @playerversion Flash 10

                     * @playerversion AIR 1.5

                     * @langversion 3.0

                     * @param importClass    The import converter class to register or null

                     * @param exportClass    The export converter class to register or null

                     * @param format         The format string tagging the converter classes

                     * @param clipboardFormat          The string used as the clipboard format when converting to/from the clipboard. Make this null if the format doesn't support clipboard access.

                     */

                    public static function addFormatAt(index:int, format:String, importerClass:Class, exporterClass:Class = null, clipboardFormat:String = null):void

3. The example in blog only includes a importer. There can also be a exporter. Importer is called when you copy, while exporter when you paste.

4. You must pay attention to the *if-condition* in importToFlow() of importer.

Please pay attention to the bold words of item 2 in my last reply. You cannot miss the fifth paramter.

TextConverter.addFormatAt(0, "plainText", PlainTextImporter, PlainTextExporter, "air:text");

Is TextConverter influences the global copy behaviours in all TextFlows?

Yes, but you can add if-conditions in importToFlow() to skip it under some circumstances.

Maybe you can refer to the code of flashx.textLayout.conversion.TextConverter,  the default importers and exporters.

The default clipboard is

static tlf_internal function setFormatsToDefault():void

{    

      _descriptors = [];     

     addFormat(TEXT_LAYOUT_FORMAT, TextLayoutImporter, TextLayoutExporter, TEXT_LAYOUT_FORMAT);     

     addFormat(TEXT_FIELD_HTML_FORMAT, TextFieldHtmlImporter,  TextFieldHtmlExporter, null);     

     addFormat(PLAIN_TEXT_FORMAT, PlainTextImporter, PlainTextExporter, "air:text");

} 

Besides, you may want to change the name of your class to avoid unexpected issues. You can see that there is already a TLF importer named PlainTextImporter.