Wysiwyg Plugin

On this page:

• Features
• Details
  • What's in the package
  • How it works
  • Using the translators from Perl scripts
  • Integrating a HTML Editor
  • Other techniques
• Plugin Installation Instructions
• Plugin Configuration Settings
  • Translator control
• Known issues
  • Incompatible with "non-standard" syntax
  • Overlapping styles
  • Rowspan processing needs TablePlugin
  • TinyMCEPlugin integration
• Plugin Info

Translator framework for WYSIWYG editors

Support for the integration of WYSIWYG (What-You-See-Is-What-You-Get) editors. On its own, the only thing this plugin gives you is a stand-alone HTML to TML (TWiki Markup Language) translator script. For WYSIWYG editing you will also need to install a specific editor package such as TinyMCEPlugin.

This plugin provides a generic framework that supports editing of topics using any browser-based HTML editor. It works by transforming TML (TWiki Markup Language) into HTML for the editor, and then transforming HTML back into TML on save.

Features

• Supports the input of malformed HTML
• Full round-trip (TML -> XHTML -> TML)
• Framework is editor-agnostic

Details

What's in the package

The package includes the following pieces:

• TML (TWiki Markup Language) to HTML translator
• HTML to TML translator (with stand-alone script)
• Generic TWiki plugin for automating the translation during editing

How it works

The plugin works by translating the topic text into HTML when someone edits a topic. The HTML is then fed to the WYSIWYG editor. On save, the edited HTML is run through the reverse translation before saving to the topic. TML is used in preference to HTML in the stored topic wherever possible, though HTML may be used if the translator can't find a suitable TML equivalent.

The default rendering that TWiki uses to generate HTML for display in browsers is 'lossy' - information in the TML is lost in the HTML output, and a round-trip (recovering the original TML from the HTML) is impossible. To solve this problem the plugin instead uses its own translation of TML to XHTML. The generated XHTML is annotated with CSS classes that support the accurate recovery of the original TML.

Before you ask the obvious question, yes, the translator could be used to replace the TWiki rendering pipeline for generating HTML pages. In fact, the translator is taken almost directly from the implementation of the rendering pipeline for the TWiki-4 release

Translation of the HTML back to TML uses the CPAN:HTML::Parser. This parser is used in preference to a more modern XML parser, because the WYSIWYG editor may not generate fully compliant XHTML. A strict parser would risk losing content. HTML::Parser is better at handling malformed HTML.

There is also the advantage that the translator can be used to import HTML from other sources - for example, existing web pages. Due to the simple nature of TML and the potential complexity of web pages, this translation is often lossy - i.e. there will be HTML features that can be entered by editors that will be lost in this translation step. This is especially noticeable with HTML tables.

Using the translators from Perl scripts

Both translators can be used directly from Perl scripts, for example to build your own stand-alone translators.

A stand-alone convertor script for HTML to TML is included in the installation. It can be found in tools/html2tml.pl.

Integrating a HTML Editor

The plugin can be used to integrate an HTML editor in a number of different ways.

1. The HTML for the content-to-be-edited can be generated directly in the standard edit template.
2. The HTML for the content-to-be-edited can be generated directly in a specialized edit template.
3. A URL can be used to fetch the content-to-be-edited from the server, for use in an IFRAME.
4. REST handlers can be called from Javascript to convert content.

Generating content directly in the standard edit template

This is the technique used by WYSIWYG editors that can sit on top of HTML textareas, such as TinyMCE. The topic content is pre-converted to HTML before inclusion in the standard edit template. These editors use plugins that have a beforeEditHandler and an afterEditHandler. These handlers are responsible for the conversion of topic text to HTML, and post-conversion of HTML back to TML.

1. User hits "edit".
2. Editor-specific plugin beforeEditHandler converts topic content to HTML by calling TWiki::Plugins::WysiwygPlugin::TranslateTML2HTML.
3. User edits and saves
4. Editor-specific plugin afterEditHandler converts HTML back to TML by calling TWiki::Plugins::WysiwygPlugin::TranslateHTML2TML.

• WysiwygPlugin should not be enabled in configure.
• WYSIWYGPLUGIN_WYSIWYGSKIN should not be set.
• Your plugin should set the textareas_hijacked context id, to signal to skins to suppress their textarea manipulation functions.

This is the recommended integration technique, if your editor can support it.

Generating content directly in a specialized edit template

This technique is useful when the editor requires the topic content in a variety of different formats at the same time. In this scenario the editor uses a custom edit template. The WYSIWYG content is made available for instantiation in that template in a number of different formats. WYSIWYGPLUGIN_WYSIWYGSKIN must be set for this to work.

The flow of control is as follows:

1. User hits "edit" with the skin (or cover) set the same as WYSIWYGPLUGIN_WYSIWYGSKIN.
2. The WysiwygPlugin beforeEditHandler determines if the topic is WYSIWYG editable, and vetoes the edit if not by redirecting to the standard edit skin. the edit
3. The edit template containing the JS editor is instantiated.
4. The following variables are available for expansion in the template:
   • %WYSIWYG_TEXT% expands to the HTML of the content-to-be-edited. This is suitable for use in a textarea.
   • %JAVASCRIPT_TEXT% expands to the HTML of the content-to-be-edited in a javascript constant.
5. User edits and saves
6. The afterEditHandler in the WyswiygPlugin sees that wysiwyg_edit is set, which triggers the conversion back to TML.

• The HTML form in the edit template must include an <input called wysiwyg_edit and set it to 1, to trigger the conversion from HTML back to TML.
• WYSIWYGPLUGIN_WYSIWYGSKIN must be set to the name of the skin used for WYSIWYG editing. This is often the name of the editor e.g. xinha.

Fetching content from a URL

In this scenario, the edit template is generated without the content-to-be-edited. The content is retrieved from the server using a URL e.g. from an IFRAME.

The flow of control is as follows:

1. As Generating content directly in a specialized edit template
2. As Generating content directly in a specialized edit template
3. As Generating content directly in a specialized edit template
4. When the document loads in the browser, the JS editor invokes a content URL (using an IFRAME or a XmlHttpRequest) to obtain the HTML document to be edited
   • The content URL is just a TWiki view URL with the wysiwyg_edit parameter set.
   • The WysiwygPlugin recognises the wysiwyg_edit parameter and uses the TML2HTML translator to prepare the text, which is then returned as text/plain to the browser.
   • Two TWiki variables, %OWEB% and %OTOPIC%, can be used in the content URL in the edit template to refer to the source topic for the content.
5. After edit handling is as for Generating content directly in a specialized edit template

Other techniques

Asynchronous saves

Editors can use XmlHttpRequest to perform saves, by POSTing to the TWiki save script with the wysiwyg_edit parameter set to 1. This parameter tells the beforeSaveHandler in the WysiwygPlugin to convert the content back to TML. See CommandAndCGIScripts for details of the other parameters to the save script.

Once the save script has completed it responds with a redirect, either to an Oops page if the save failed, or to the appropriate post-save URL (usually a view). The editor must be ready to handle this redirect.

Handling Attachments

Attachment uploads can be handled by URL requests from the editor template to the TWiki upload script. The upload script normally redirects to the containing topic; a behavior that you usually don't want in an editor! There are two ways to handle this:

• If the uploads are done in an IFRAME or via XmlHttpRequest, then the 302 redirect at the end of the upload can simply be ignored.
• You can pass noredirect to the upload script to suppress the redirect. In this case you will get a text/plain response of OK followed by a message if everything went well, or an error message if it did not.

REST handlers

If you are confident in Javascript you can use REST handlers with XmlHttpRequest to convert content from TML to HTML and back again.

The plugin defines the following REST handlers:

.../rest/WysiwygPlugin/html2tml?topic=Web.Topic;text=htmltexttotranslate

Converts the HTML text to TML. topic must be specified.

.../rest/WysiwygPlugin/tml2html?topic=Web.Topic;text=tmltexttotranslate

Converts the TML text to HTML. topic must be specified. The response is a text/plain page of converted content.

Plugin Installation Instructions

This plugin is pre-installed. TWiki administrators can upgrade the plugin as needed on the TWiki server.

Plugin Configuration Settings

Translator control

The global TWiki Variable WYSIWYG_EXCLUDE can be set to make the plugin sensitive to what is in a topic, before allowing it to be edited. You can set it up to veto an edit if the topic contains:

• html - HTML tags (e.g. <div>, not including <br>), or
• variables - simple variables (e.g. %VAR%) or
• calls - TWiki variables with parameters e.g. %VARIABLE{...}%
• pre blocks (<pre>)
• HTML comments (<!-- ... -->)

If the plugin detects an excluded construct in the topic, it will refuse to allow the edit and will redirect to the default editor.

If you excluded calls in WYSIWYG_EXCLUDE, you can still define a subset of TWiki variables that do not block edits. this is done in the global TWiki variable WYSIWYG_EDITABLE_CALLS, which should be a list of TWiki variable names separated by vertical bars, with no spaces, e.g: * Set WYSIWYG_EDITABLE_CALLS = COMMENT|CALENDAR|INCLUDE

You should set WYSIWYG_EXCLUDE and WYSIWYG_EDITABLE_CALLS in TWikiPreferences, or in WebPreferences for each web.

You can define the global variable WYSIWYGPLUGIN_STICKYBITS to stop the plugin from ever trying to convert specific HTML tags into HTML when certain specific attributes are present on the tag. This is most useful when you have styling or alignment information in tags that must be preserved.

This variable is used to tell the translator which attributes, when present on a tag, make it "stick" i.e. block conversion. For example, setting it to table=background,lang;tr=valign will stop the translator from trying to handle any table tag that has background or lang attributes, and any tr tag that has a valign attribute.

You can use perl regular expressions to match tag and attribute names, so .*=id,on.* will ensure that any tag with an on* event handler is kept as HTML.

The default setting for this variable is:

    .*=id,lang,title,dir,on.*;
    A=accesskey,coords,shape,target;
    BDO=dir;
    BR=clear;
    COL=char,charoff,span,valign,width;
    COLGROUP=align,char,charoff,span,valign,width;
    DIR=compact;
    DIV=align;
    DL=compact;
    FONT=size,face;
    H\d=align;
    HR=align,noshade,size,width;
    LEGEND=accesskey,align;
    LI=type,value;
    OL=compact,start,type;
    P=align;
    PARAM=name,type,value,valuetype;
    PRE=width;
    Q=cite;
    TABLE=align,bgcolor,border,cellpadding,cellspacing,frame,rules,summary,width;
    TBODY=align,char,charoff,valign;
    TD=abbr,align,axis,bgcolor,char,charoff,colspan,headers,height,nowrap,rowspan,scope,valign,width;
    TFOOT=align,char,charoff,valign;
    TH=abbr,align,axis,bgcolor,char,charoff,colspan,height,nowrap,rowspan,scope,valign,width,headers;
    THEAD=align,char,charoff,valign;
    TR=bgcolor,char,charoff,valign;
    UL=compact,type

If you edit using the plain-text editor, you can use the <sticky>..</sticky> tags to delimit HTML (or TML) that you do not want to be WYSIWYG edited.

Implementors note: If you are using your own before/after edit handlers, you can call TWiki::Plugins::WysiwygPlugin::isWysiwygEditable() to check these controls.

Known issues

Incompatible with "non-standard" syntax

The WysiwygPlugin is incompatible with plugins that expand non-standard syntax e.g. TWiki:Plugins.MathModePlugin (WysiwygPlugin)

Plugins that extend the syntax using TWiki variables, such as %MYVARIABLE%, should work fine.

Implementors note: Plugins that use XML-like tags may call TWiki::Plugins::WysiwygPlugin::addXMLTag() from their initPlugin handlers to make the WysiwygPlugin protect the content between XML-like tags, just like it does for TWiki variables.

Overlapping styles

Because TWiki uses a "best guess" approach to some formatting, it allows overlapping of tags in a way forbidden by HTML, and it is impossible to guarantee 100% that formatting in the original TWiki document will still be there when the same document is loaded and then saved through the WysiwygPlugin. The most obvious case of this is to do with styles. For example, the sentence

*bold _bold-italic* italic_

is legal in TML, but in HTML is represented by

<strong>bold <em>bold-italic</em></strong> <em>italic</em>

which gets translated back to TML as

*bold _bold-italic_* _italic_

which is correct by construction, but does not render correctly in TWiki. This problem is unfortunately unavoidable due to the way TML works.

Rowspan processing needs TablePlugin

The WysiwygPlugin is able to convert tables with cells that span rows into TML. This requires syntax provided by the TablePlugin (that is, the | ^ | markup). the WysiwygPlugin will therefore only perform row-span related conversion if the TablePlugin is enabled. The TablePlugin is enabled by default and hence the WysiwygPlugin converts tables with cells that span rows between TML and HTML by default.

If the TablePlugin is not enabled, then TML table cells containing only ^ are not converted to rowspans, and HTML tables containing rowspans are not converted to TML.

TinyMCEPlugin integration

• Anchors are not handled by WysiwygPlugin
• WysiwygPlugin fails to roundtrip tables with align="center", border attributes, etc.
  • Description: Sometimes tables will fail to be converted to TML syntax (will stay as HTML) because there are attributes on the table (such as alignment or border decorations) that the WysiwygPlugin does not know how to preserve. If such attributes are necessary, please use VarTABLE instead.
  • Work-around:
    • Click inside the problematic table
    • Click the table toolbar button (usually used to create a new table)
    • With the exception of Cols and Rows, delete/reset all content from the fields on the 'General' and 'Advanced' tabs.
    • Write a VarTABLE variable above the offending table that adds the desired attributes safely

Plugin Info

Author:	Crawford Currie, TWiki Contributors
Copyright	© 2005 ILOG http://www.ilog.fr © 2007 Twiki, Inc. © 2008-2012 Foswiki Contributors © 2005-2019 Peter Thoeny and TWiki:TWiki.TWikiContributor
License	GPL (Gnu General Public License)
Sponsors:	ILOG, Carrier Corporation, Twiki Inc, Wave Systems Corp
Plugin Version:	2019-05-01

Dependencies:	Name Version Description HTML::Parser >=3.28 Required. Available from CPAN. HTML::Entities >=1.25 Required. Available from CPAN. Encode >=2.01 Required.
Plugin Home:	http://twiki.org/cgi-bin/view/Plugins/WysiwygPlugin
Feedback:	http://twiki.org/cgi-bin/view/Plugins/WysiwygPluginDev
Appraisal:	http://twiki.org/cgi-bin/view/Plugins/WysiwygPluginAppraisal

Related Topics: WysiwygPluginSettings, WysiwygPluginTopicLister, TinyMCEPlugin, TWikiPreferences, TWikiPlugins