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'
...
....