Access documents by research topic. Word searches are available through 11 categories of subjects that recur systematically in the Opera sources, presented in the menu of the left navigation bar.

This second search mode by subjects, which supplements the guided research structure of Topics1, enables the user to find all the words present in the specification text strings compiled for each category. It should be noted that specification texts are available only for those cases in which the sources themselves furnish information beyond that already implicit in the basic hierarchical structures of guided research.

Furthermore in cases in which a given specification text has been provided for more than one subcategory of the 11 principal topics, the system will present as many hits as occurrences of the specification without showing the separate fields to which they have been attributed, which will be apparent only from the individual document entry.