There is no limit on the number of transformers.
There is no meaningful performance consideration.
Transformers are not executed concurrently. The documentation implies that they are but they are not. The section in the documentation is explaining how the order of transformer execution is not defined and to “assume that [IS] concurrently executes the transformers at run-time.” Thus, they imply that they are but they don’t explicitly state that they are. Experience of many is that they are not.
If one thinks about the implications of running each transformer in a thread one quickly concludes that doing so would be overhead intensive for little/to no gain. For example, a common use for transformers is to help translate data from one form to another. To be able to set the data into a target document, threads would need to be synchronized. The overhead for managing this would quickly outweigh any supposed performance gains.
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