Link to Jakarta EL instead of mentioning Unified EL in SpEL overview

As a bit of trivia, Jakarta EL was originally Unified EL, which was
originally JSP EL, which was originally SPEL.

SPEL: Simplest Possible Expression Language
SpEL: Spring Expression Language

So one could say that SPEL inspired SpEL.

framework-docs/modules/ROOT/pages/core/expressions.adoc

@@ -1,10 +1,11 @@
 [[expressions]]
 = Spring Expression Language (SpEL)
 
-The Spring Expression Language ("`SpEL`" for short) is a powerful expression language that
+The Spring Expression Language ("SpEL" for short) is a powerful expression language that
 supports querying and manipulating an object graph at runtime. The language syntax is
-similar to Unified EL but offers additional features, most notably method invocation and
-basic string templating functionality.
+similar to the https://jakarta.ee/specifications/expression-language/[Jakarta Expression
+Language] but offers additional features, most notably method invocation and basic string
+templating functionality.
 
 While there are several other Java expression languages available -- OGNL, MVEL, and JBoss
 EL, to name a few -- the Spring Expression Language was created to provide the Spring