BUG #15474: Special character escape sequences need better documentation, or more easily found documentation

The following bug has been logged on the website:

Bug reference: 15474
Logged by: Micheal Taylor
Email address: bubthegreat(at)gmail(dot)com
PostgreSQL version: 11.0
Operating system: Any
Description:

When looking for postgresql documentation on characters that need to be
escaped, and how to escape them, I consistently get to this page:

https://www.postgresql.org/docs/current/static/sql-syntax-lexical.html#SQL-SYNTAX-SPECIAL-CHARS

That page goes over high levels of escaping numerous things, but in the
special characters and operators, it doesn't clearly show how to escape the
operators or special characters within a more complicated query structure.
For example, if I have the following table:

CREATE TABLE IF NOT EXISTS {tablename}
(
time TIMESTAMP,
case_number VARCHAR(25),
jira VARCHAR(25),
status VARCHAR(25),
fqdn VARCHAR(255),
subject TEXT,
description TEXT,
comment TEXT
)

And the following insertion information:

INSERT INTO orphans(time, case_number, fqdn, status, subject,
description)
SELECT '{timestamp}', '{case_number}', '{fqdn}', 'new', '{subject}',
'{description}'
WHERE
NOT EXISTS (
SELECT case_number, status FROM orphans
WHERE case_number = '{case_number}'
)

Where all columns inputs are strings, if any of those inputs have special
characters like % or ', it is not clear by quick inspection of the
documentation how to escape those characters. A simple table elaborating on
the escapes for each special character would be incredibly helpful at
determining how to translate those escapes for cleaning strings prior to
insertion so those of us using postgresql can quickly write cleaning
functions for data.