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nextflow/docs/developer/nextflow.extension.md

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+
+# `nextflow.extension`
+
+The `nextflow.extension` package implements the channel operators and other extension methods.
+
+## Class Diagram
+
+```{mermaid} diagrams/nextflow.extension.mmd
+```
+
+```{note}
+Some classes may be excluded from the above diagram for brevity.
+```
+
+## Notes
+
+Operators are implemented using the [GPars](http://gpars.org/1.2.1/guide/guide/dataflow.html) dataflow library. In general, an operator consumes one or more `DataflowReadChannel`s and produces one or more `DataflowWriteChannel`s. See {ref}`operator-page` for details about each operator.
+
+Other notable classes include `Bolts` and `FilesEx`, which implement various extension methods used throughout the Nextflow codebase. If you see a method that doesn't appear to be implemented by the calling object, it may be implemented in one of these extension classes.