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These problems can be grouped into three categories : syntax , combination , and vocabulary . As they have a place of pride in most descriptions of English syntax , it is appropriate to begin with sentences . The current project emphasis is on improving the effectiveness of visual syntaxes by borrowing a concept from functional programming , namely higher-order functions , and on aiding design of domain-specific visual syntaxes through met modeling . It is a namespace-aware document that uses namespaces to identify the core syntax and additional syntaxes introduced to the page through tag libraries . Almost without exception these social bookmarking tools are feature-rich , providing search on both users and tags ( with Boolean operators ) , comments ( and comment trails ) , simple linking syntaxes , and APIs ( application programming interfaces ) for posting to and from these tools ( and to other tools such as blogs ) . This was a particularly powerful combination , since a core component of Spring was the use of " contracts " to specify interface syntax . ) This parallel treatment of nonterminals conveys the relationship between the two syntaxes . Added call to invalidate_current_state ( ) in syntax_clear ( ) . In these circumstances , it is usually best to make the middle subroutine anonymous , using the sub { } syntax .