1. A method for grouping related program sequences in a plurality of groupable program flow documents for performing a task, said method comprising: providing a plurality of groupable program flow documents to be executed by a group program sequence engine; establishing, using a first code for grouping, a group that can be formed between multiple related group-elements obtained from multiple groupable program flow documents of said plurality of groupable program flow documents; and executing, using said group sequence engine, said plurality of groupable program flow documents for performing said task, wherein the executing the plurality of groupable program flow documents proceeds as a serially executed sequence of group-elements of the plurality of groupable program flow documents, and the executing comprises: establishing the group as a candidate union of the multiple related group-elements; subsequent to executing at least one group-element in the serially executed sequence of group-elements of the plurality of groupable program flow documents, reaching a point of execution of the serially executed sequence at which a single group-element of the multiple related group-elements is selected to be executed in the serially executed sequence, the point of execution reached in executing group-elements of one groupable program flow document of the plurality of groupable program flow documents; determining whether the single group element is part of a potential union of group-elements, wherein it is determined, based on the establishing the group as a candidate union, that the single group elements is part of a potential union of group-elements; based on determining that the single group-element is part of a potential union of group-elements, validating the candidate union to form a validated union of group-elements in which the single group-element of the multiple related group-elements is to execute rather than executing the multiple related group-elements; based on the validating, determining whether any related group-element of the multiple related group-elements has associated therewith an ancestor group-element that has not yet been executed as part of the serially executed sequence and that is to be executed before executing the single group-element, the ancestor group-element being an element of another groupable program flow document, of the plurality of groupable program flow documents, to which the related group-element belongs, and the ancestor group-element being outside of the group of multiple related group-elements, wherein it is determined that at least one related group-element of the multiple related group-elements has associated therewith at least one ancestor group-element that has not yet been executed as part of the serially executed sequence and that is to be executed before executing the single group-element; based on determining that the at least one related group-element has associated therewith at least one ancestor group-element that has not yet been executed as part of the serially executed sequence and that is to be executed before executing the single group-element, initiating execution of the at least one ancestor group-element associated with the at least one related group-element; and subsequently executing the single group-element, based on execution of the at least one ancestor group-element, wherein the single group-element of said group is executed only once during execution of said plurality of groupable program flow documents.