In general, you will find Spring EL, Unified EL and OGNL to have a very similar syntax.
Note however there are some advantages to Spring EL. For example Spring EL is closely integrated with the type conversion of Spring 3 and that allows you to take full advantage of its features. Specifically the automatic detection of generic types as well as the use of formatting annotations is currently supported with Spring EL only.
There are some minor changes to keep in mind when upgrading to Spring EL from Unified EL or OGNL as follows:
Expressions deliniated with ${} in flow definitions must be changed to #{}.
Expressions testing the current event #{currentEvent == 'submit'} must be changed to #{currentEvent.id == 'submit'}.
Resolving properties such as #{currentUser.name} may cause NullPointerException without any checks such as #{currentUser != null ? currentUser.name : null}.
A much better alternative though is the safe navigation operator #{currentUser?.name}.
For more information on Spring EL syntax please refer to the Language Reference section in the Spring Documentation.