Document that character length limits of UNICODE_FSS are enforced

src/docs/asciidoc/en/rlsnotes/rlsnotes40/_compatibility-40.adoc

@@ -216,6 +216,14 @@ Now a sequence is created (or restarted) with its current value set to its start
 
 If some `INSERT` statement contains a `RETURNING` clause that refers columns of the underlying table, the appropriate `SELECT` privilege must be granted to the caller.
 
+[[rnfb40-compat-sql-unicode-fss]]
+=== UNICODE_FSS Character Length
+
+Firebird now enforces the character length limits of UNICODE_FSS columns.
+It is no longer possible to store oversized strings in columns with character set UNICODE_FSS.
+
+See also <<rnfb40-unicode-fss-limit,Character Limit Enforced for UNICODE_FSS>>.
+
 [[rnfb40-compat-utils]]
 == Utilities
 

src/docs/asciidoc/en/rlsnotes/rlsnotes40/_engine-40.adoc

@@ -1335,3 +1335,12 @@ Columns:
 
 Table RDB$CONFIG is populated from in-memory structures upon request and its instance is preserved for the SQL query lifetime.
 For security reasons, access to this table is allowed to administrators only. Non-privileged users see no rows in this table (and no error is raised).
+
+[[rnfb40-unicode-fss-limit]]
+== Character Limit Enforced for UNICODE_FSS
+
+The character length limit is now enforced for UNICODE_FSS.
+Historically, Firebird did not check the character length limit of UNICODE_FSS columns, only the total byte length.
+Attempts to store values longer than the declared length into a column with character set UNICODE_FSS, will now fail with a "`string right truncation`" error.
+
+NOTE: This has been the case since Firebird 4.0.0, but was not documented until the release notes of Firebird 4.0.3.