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Introduction

plone.outputfilters provides a framework for registering filters that get applied to text as it is rendered.

By default, these filters are wired up to occur when text is transformed from the text/html mimetype to the text/x-html-safe mimetype via the PortalTransforms machinery.

With the RichText field of plone.app.textfield, this transform is typically applied when the field value is first accessed. The result of the transform is then cached in a volatile attribute for an hour or until the value is replaced.

Included Filters

A default filter is included which provides the following features:

  • Resolving UID-based links
  • Adding captions to images

(These are implemented as one filter to avoid the overhead of parsing the HTML twice.)

These features used to be provided by similar transforms in both Products.kupu and Products.TinyMCE. New releases of these editors are being prepared which depend on the transform in plone.outputfilters, so that bugs don't need to be fixed in multiple places.

Resolving UID-based links

Internal links may be inserted with a UID reference rather than the real path of the item being linked. For example, a link might look like this:

<a href="resolveuid/6992f1f6-ae36-11df-9adf-001ec2a8cdf1">

Such URLs can be resolved by the resolveuid view, which resolves the UID to an object and then redirects to its URL. However, resolving links in this way requires an extra request after the redirect. The resolveuid filter avoids that by replacing such URLs with the object's actual full absolute URL as the link is rendered.

UIDs are resolved using plone.app.uuid.utils.uuidToURL.

The resolveuid filter is enabled if there is at least one plone.outputfilters.filters.resolveuid_and_caption.IResolveUidsEnabler utility whose available property returns True. This mechanism exists for compatibility with TinyMCE and kupu, which both provide their own control panel setting to enable the link-by-uid feature.

Image captioning

Image tags with the "captioned" class and a src attribute that resolves to an image object within the site will be wrapped in a definition list (DL) tag which includes a caption based on the value of the image's description field, if any.

For example, this image tag:

<img src="path/to/image" class="captioned"/>

might be transformed into:

<dl class="captioned">
 <dt><img src="path/to/image"/></dt>
 <dd class="image-caption">Caption text</dd>
</dl>

assuming the image found at "path/to/image" has the description "Caption text".

The captioning filter is enabled if there is at least one plone.outputfilters.filters.resolveuid_and_caption.IImageCaptioningEnabler utility whose available property returns True. This mechanism exists for compatibility with TinyMCE and kupu, which both provide their own control panel setting to enable the captioning feature.

The captioned version of an image is rendered using the @@plone.outputfilters_captioned_image view, which may be overridden to customize the caption. This view is passed the following kwargs:

class
The CSS class on the image.
originalwidth
The width attribute of the image tag.
originalalt
The alt attribute of the image tag.
url_path
The path of the image, relative to the site root.
caption
The image's description.
image
The (possibly scaled) image object.
fullimage
The original unscaled image object.
tag
A full HTML tag which displays the image.
isfullsize
True if image is fullimage.
width
The width of image.