4.1. Lexical Structure

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Page: https://www.postgresql.org/docs/18/sql-syntax-lexical.html
Description:

Why repeat information within the same section?

In Section 4.1.1, “Identifiers and Keywords”:

The option with identifiers in quotation marks allows you to include

escaped Unicode characters identified by their code points. This option
begins with U& (an uppercase or lowercase U followed by an ampersand)
immediately before the opening double quotation mark, with no spaces between
them, for example, U&“foo”. (Note that this creates ambiguity regarding the
& operator. To avoid this problem, use spaces around the operator.) Inside
the quotation marks, Unicode characters can be specified in escaped form by
writing a backslash followed by the character’s four-digit hexadecimal code,
or, alternatively, a backslash followed by a plus sign, followed by the
character’s six-digit hexadecimal code. For example, the identifier “data”
can be written as follows:

U&“d\0061t\+000061”

...
....

This information, along with examples, is also provided in Section 4.1.2.3.
String Constants with Escaped Unicode Characters

PostgreSQL also supports another type of string escape syntax that allows

you to specify arbitrary Unicode characters by code point. A Unicode-escaped
string constant begins with U& (an uppercase or lowercase U followed by an
ampersand) immediately before the opening quote, with no spaces between
them, for example, U&“foo”. (Note that this creates ambiguity with the &
operator. To avoid this problem, use spaces around the operator.) Inside the
quotes, Unicode characters can be specified in escaped form by writing a
backslash followed by the four-digit hexadecimal code of the character, or,
alternatively, a backslash followed by a plus sign, followed by the
six-digit hexadecimal code of the character. For example, the string “data”
can be written as follows:

U&'d\0061t\+000061'

...
....