1. A method of simplifying development of user interfaces of applications, said method comprising: maintaining a plurality of specifications of user interfaces provided by a plurality of applications, each of said plurality of specifications containing interface definitions of all of a corresponding set of UI (user interface) elements in the respective user interface, said plurality of specifications containing a first specification and a second specification respectively of a first user interface and a second user interface provided by a first application of said plurality of applications, wherein said second user interface is identified by a second identifier, wherein said first specification contains a link to said second identifier associated with an UI element to indicate that said second user interface is designed to be accessible from said first user interface based on a user action associated with said UI element of said first user interface, wherein said second specification is rendered to provide said second user interface upon said user action associated with said UI element in said first user interface; receiving from a developer, input data indicating selection of said first user interface; inspecting, in response to said receiving, said first specification to determine that said second user interface is accessible from said first user interface based on said link; displaying on a display unit, in response to only said input data, both of said first user interface and said second user interface in view of said second user interface being determined to be accessible from said first user interface, said first user interface having a first set of UI elements and said second user interface having a second set of UI elements, wherein said first set of UI elements and said second set of UI elements are selectable for inclusion in development of new user interfaces in response to only said input data; receiving, from said developer, a first indication that a first UI element from said first set of UI elements and a second UI element from said second set of UI elements are to be included in a new user interface of a new application, wherein said first indication is generated upon said developer selecting said first UI element and said second UI element displayed on said display unit; and creating a new specification for said new user interface incorporating the interface definitions of said first UI element and said second UI element, the interface definitions of said first UI element and said second UI element being retrieved respectively from said first specification and said second specification, wherein said receiving further receives a second indication that all UI elements of said first user interface are to be included in said new user interface, in response to said second indication, said creating incorporating in said new specification the interface definitions of all of said first set of UI elements retrieved from said first specification.