Add docs for SRF column accessors

Fixes #3070.

v2.1/table-expressions.md

@@ -186,7 +186,7 @@ For example:
 
 {% include copy-clipboard.html %}
 ~~~ sql
-> SELECT * FROM generate_series(1, 3)
+> SELECT * FROM generate_series(1, 3);
 ~~~
 ~~~
 +-----------------+
@@ -198,7 +198,30 @@ For example:
 +-----------------+
 ~~~
 
-{{site.data.alerts.callout_info}}Currently CockroachDB only supports a small set of generator function compatible with <a href="https://www.postgresql.org/docs/9.6/static/functions-srf.html">the PostgreSQL set-generating functions of the same name</a>.{{site.data.alerts.end}}
+<span class="version-tag">New in v2.1:</span> Set-returning functions (SRFs) can now be accessed using `(SRF).x` where `x` is one of the following:
+
+- The name of a column returned from the function
+- `*` to denote all columns.
+
+For example (note that the output of queries against [`information_schema`](information-schema.html) will vary per database):
+
+{% include copy-clipboard.html %}
+~~~ sql
+> SELECT (i.keys).* FROM (SELECT information_schema._pg_expandarray(indkey) AS keys FROM pg_index) AS i;
+~~~
+
+~~~
+ x | n
+---+---
+ 1 | 1
+ 2 | 1
+(2 rows)
+~~~
+
+{{site.data.alerts.callout_info}}
+Currently CockroachDB only supports a small set of generator functions compatible with [the PostgreSQL set-generating functions with the same
+names](https://www.postgresql.org/docs/9.6/static/functions-srf.html).
+{{site.data.alerts.end}}
 
 ## Operators that extend a table expression