Recursion of Address_Match_List

syn match xyz_Semicolon contained /;/ skipwhite skipempty
\ containedin=xyz_AML

syn match xyz_Number contained "\<\d\{1,10}\>" skipwhite skipempty
\ nextgroup=xyz_Semicolon
\ containedin=xyz_AML

" { ... }  ;
syn region xyz_AML contained start=+{+ end=+}+ skipwhite skipempty
\ nextgroup=
\    xyz_Number,
\    xyz_Semicolon

" <acl_name> ( <number> | { ... } ) ;
syn match xyz_ACLIdent contained /\<[0-9a-zA-Z\-_]\{1,63}\>/ skipwhite
\ nextgroup=
\    xyz_AML,
\    xyz_Number

syn match xyz_Keywords /\_^\s*\<acl\>/ skipempty skipwhite
\ nextgroup=xyz_ACLIdent