Clarification on materialized view restriction needed

Hi All,
I want to create a materialized view as the output of a plpgsql function
returning a set of rows. But that function creates temporary tables and
thus can not be used for creating materialized view as per the
documentation at
http://www.postgresql.org/docs/9.3/static/sql-creatematerializedview.html.
"This query will run within a security-restricted operation; in particular,
calls to functions that themselves create temporary tables will fail."

I tried to understand what is "security-restricted operation", and didn't
find any definition of this term or any listing as to "these are
security-restricted operations ...". I am wondering what are other
restrictions on the queries whose results can be used to create
materialized views.

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Best Wishes,
Ashutosh Bapat
EntepriseDB Corporation
The Postgres Database Company