Difference between Spring Expression Language (SpEL) and Unified Expression Language (UEL)

What are the differences between <expression w760> Expression Language (SpEL) and Unified Expression Language (UEL)?

Spring's official documentation says:

"The language syntax is similar to Unified EL, but offers additional functions, primarily method calls and basic template template functions." (see http://static.springsource.org/spring/docs/current/spring-framework-reference/html/expressions.html )

What exactly are the differences in the method call?

Are there any other differences?

thanks Matthias