Yes, that is perfectly valid. See here.
Also, from the (draft) standard 2.14.5/4:
A source-file new-line in a raw string literal results in a new-line
in the resulting execution string-literal. Assuming no whitespace at the beginning of lines in the
following example, the assert will succeed:
const char *p = R"(a
b
c)";
assert(std::strcmp(p, "a\
b
c") == 0);
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