String syntax changed?

[Roland Orre]

In guile-1.6 and earlier versions, the following
        (begin (display "$\\scriptstyle{P(A\|D)}$") (newline))
gives the intentional string:
        $\scriptstyle{P(A|D)}$

but in 1.7 I get:
ERROR: In procedure scm_lreadr:
ERROR: #<unknown port>:1:38: illegal character in escape sequence: #\|
ABORT: (read-error)
ERROR: Unbound variable: D
ABORT: (unbound-variable)
ERROR: In procedure scm_lreadr:
ERROR: #<unknown port>:1:40: unexpected ")"
ABORT: (read-error)
ERROR: Unbound variable: }$
ABORT: (unbound-variable)

There it seems as \| has a special meaning
and the following gives the intentional string:

(begin (display "$\\scriptstyle{P(A|D)}$") (newline))

I don't understand. Can someone hint me about documentation about this?
Fortunately "|" still works in older versions.

        Roland Orre