psql meta-command string interpolation differs from SQL

Mostly looking for affirmation though it was somewhat surprising that I had
no recollection of this dynamic even though I've been a fairly avid reader
of the documentation.

Executing the following in psql:

\set name_regexp '^\S+'
CREATE TABLE testtbl ( textid NOT NULL PRIMARY KEY CHECK (textid ~
:'name_regexp');

The constraint that ends up being saved is:

textid ~ '^S+'

This is a default 9.3 box. Typically I write my SQL literal regular
expressions without E'' in order to avoid escaping all of the
back-slashes. It seemed that using \set would be useful since I am using
psql to execute the DDL anyway.

psql --file ^^^

Any thoughts or suggestions?

At what point is the "\S" that I wrote being turned into an escaped "S"?
By the "\set" before going into the variable or at the :'name_regexp'
output conversion? Not that it likely matters to me, the end-user. It
would aid in deciding where it might be possible to introduce new syntax,
like the E'' that SQL uses, to gain a measure of conformity.

TIA

David J.