I found a nice update in FME 2014. That is "Edit Attribute" tool for Transformers.
This article is describing about the tool for Writers.
> FME 2014 Sneak Peek: Top 10 Workbench Optimizations > 5 Edit Attribute Value
But this tool can be also used for every Transformer.
2014-02-07: Related documentation > Inserting Attributes to Transformer Outputs
First of all, let's confirm when new attributes created by this tool will be added to the input feature. Before processing or After processing of the transformer? (pre-process or post-process?)
By the analogy from the previous functionality i.e. "Add Attribute" + "Insert Constant", it's expected that new attributes would be added After processing.
OK, indeed new attributes have been added After processing of the transformer.
The followings are practical use cases which I thought of immediately. Of course all of them can be replaced with existing transformers, but using the "Edit Attribute" tool can make the workspace more concise.
Calculate Width and Height of Bounding Box in a BoundsExtractor
-- surrogate for an AttributeCreator or two ExpressionEvaluator etc.
Extract First Element of List Attribute in an AttributeSplitter
-- surrogate for a ListIndexer etc.
Calculate Length of Line Geometry in a VertexCreator
-- surrogate for a LengthCalculator etc.
Interesting. The "Edit Attribute" tool can be used as something like Expanding Transformer Functionality. There should be many effective use cases.
The "Edit Attribute" tool looks like a pretty baby of the AttributeCreator. I love it :-)