get the valid text editor extension which is calcualte from the CONFIG_EDITABALE_VALID_EXTS exclude those specified in CONFIG_UPLOAD_INVALID_EXTS and those are not specified in CONFIG_UPLOAD_VALID_EXTS
array getValidTextEditorExts()- Function name: getValidTextEditorExts
- Source: admin-dev/ajaxfilemanager/inc/function.base.php line 721.