DITA Semantics Potentially Affected by Filtering

[ekimber <ekimber@reallysi.com>]

Here is my attempt to analyze the effect of filtering on DITA processing
semantics. Note that the Open Toolkit does filtering before any other
processing, so it always reflects the results of applying filtering first.

My initial instinct was that only keyspace construction was affected by
application of filtering. It appears I was completely wrong. My analysis,
given below, is that every significant processing semantic will give
significantly different results when filtering is applied first and when it
is not.

I think this is a complete list of relevant processing semantics. Note that
I'm only considering processing that is intended to have invariant results
(that is, it's not a rendition option but a DITA-defined semantic).

1. Keyref 

A given key may be the effective key when filtering is applied and not the
effective key when filtering is not applied.

* Filtering is significant

2. Content reference

When "-dita-use-conref-target" is *not* used, a referencing element will be
filtered out before or after conref resolution, because its applicability is
not modified.

When "-dita-use-conref-target" *is* used and the referenced element has a
different applicability, the referencing element can filtered differently
following conref resolution than before. If the referenced element is
filtered out, the effect of the conref if filtering is applied before
resolution is that the content reference cannot be resolved and the
referencing element is unmodified in the resolved result. If filtering is
applied after conref resolution, then the resolved result is filtered out,
resulting in no element at all in the resolved and filtered result.

* Filtering is significant

3. XRef resolution

If an xref is resolved to its target before filtering and the target is
subsequently filtered out, the xref would be to a non-existent target but
might reflect properties of the target (e.g., the xref link text might
reflect the target's title). If the xref is resolved after filtering is
applied and the target is filtered out, the xref is to a non-existent
target, which will can result in a different link text. The rendition effect
for the navigation link will be the same: the link cannot be navigated
because the target doesn't exist in the rendered result.

* Filtering is significant for link text, not significant for link
navigation

4. Map metadata propagation

Filtering applied before propagation could definitely result in different
effective values than if it is applied after. In particular, elements
filtered out would never contribute to propagation.

* Filtering is significant

5. Topicref resolution

Same analysis as for xref: resolution of topicrefs before filtering could
result in use of topic-provided navigation titles or metadata that would not
be used if the target topic was filtered out before resolution. In both
cases, the topicref as rendered would be to a missing topic.

* Filtering is significant

6. Chunking

A topicref subsequently filtered out that generates chunks would create
chunks in the output if chunk processing is done before filtering but since
the topicref would then be filtered out, the chunks would not be referenced.

* Filtering is significant

7. @copy-to

If copy-to processing is done before filtering, two topicrefs, only one of
which is applicable, could specify the same copy-to target, leading to a
conflict and a potential ambiguity about which governs. If the topicrefs are
filtered before copy-to processing, the conflict cannot occur.

NOTE: The current spec does not say what happens when two topicrefs specify
the same copy-to value.

* Filtering is significant

Cheers,

Eliot

----
Eliot Kimber | Senior Solutions Architect | Really Strategies, Inc.
email:  ekimber@reallysi.com <mailto:ekimber@reallysi.com>
office: 610.631.6770 | cell: 512.554.9368
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