davidwrede commented on a change in pull request #13317:
URL: https://github.com/apache/beam/pull/13317#discussion_r523299244
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File path: website/www/site/content/en/documentation/programming-guide.md
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@@ -5431,4 +5431,280 @@ use case.
{{< highlight py >}}
{{< code_sample "sdks/python/apache_beam/examples/snippets/snippets.py"
BundleFinalize >}}
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+{{< /highlight >}}
+
+## 13. Multi-language pipelines {#mulit-language-pipelines}
+
+Beam allows you to combine transforms written in any supported SDK language
(currently, Java and Python) and use them in one multi-language pipeline. This
capability makes it easy to provide new functionality simultaneously in
different Apache Beam SDKs through a single cross-language transform. For
example, the [Apache Kafka
connector](https://github.com/apache/beam/blob/master/sdks/python/apache_beam/io/kafka.py)
and [SQL
transform](https://github.com/apache/beam/blob/master/sdks/python/apache_beam/transforms/sql.py)
from the Java SDK can be used in Python streaming pipelines.
+
+Pipelines that use transforms from more than one SDK-language are known as
*multi-language pipelines*.
+
+### 13.1. Creating cross-language transforms {#create-x-lang-transforms}
+
+To make transforms written in one language available to pipelines written in
another language, an *expansion service* for that transform is used to create
and inject the appropriate language-specific pipeline fragments into your
pipeline.
Review comment:
Added clarification.
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