[annotator-dev] Anchoring tolerance to annotated content edits

[Randall Leeds]

On Fri, Sep 29, 2017 at 10:01 AM Cloutier, Philippe (DGARI-Consultant) <
Philippe.Cloutier.externe at mern-mffp.gouv.qc.ca> wrote:

> Hi,
> Tiki Wiki CMS Groupware has an experimental integration of annotator.js
> which I am testing. The basics are working. The big problem is we're
> annotating wiki pages which frequently change, so anchoring robustness
> needs to be reasonably good.
>

I noticed you also asked about anchoring on the Hypothesis mailing list.
I'll let most of the discussion happen there as it is a more active project
than Annotator.js, and it is designed to address this issue.


>
> Apparently, after a change, annotations are not displayed somewhere they
> should not, which is great. Unfortunately, after a change, there is a high
> risk that an annotation "disappears" (stops being displayed). Annotator's
> anchoring strategy seems to be to record start and end offsets on the
> annotated text's containing elements and to record the annotated text. If
> the annotated text changes its position in its containing element or if the
> containing element's path changes, the annotation stops displaying. Which
> means that several common changes have a nearly 50% chance of breaking
> anchoring:
> 1. Fixing a typo in the annotated text's parent elements.
> 2. Adding, removing or moving a sibling (such as a paragraph) of the
> parent elements.
>


Annotator does use a DOM Range representation consisting of document nodes
and offsets. There is no easy way to change this.


> Am I missing a document on Annotator's anchoring robustness acknowledging
> this situation and/or suggesting ways to increase tolerance to
> modifications of the annotated content?
>

You did not miss anything. This is a known limitation of Annotator.js. It
was not originally designed for this use case.

I have stopped working on Annotator.js in order to focus the limited
availability I have for annotation projects on Apache Annotator (
https://annotator.apache.org). Hypothesis uses a number of standalone
libraries for anchoring, most of which should find their way into the
Apache Annotator umbrella.

https://github.com/tilgovi/dom-anchor-text-position
https://github.com/tilgovi/dom-anchor-text-quote
https://github.com/openannotation/xpath-range

You may use these to implement your own annotation tools if Hypothesis
turns out to be difficult to customize to your needs. However, I hope that
Hypothesis will be able to satisfy your use case, as that would be the
easiest road.
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