Mark parts of an input as literal or general 2 Annotate parts of synthesized programs to be desired or undesired 3 View other similar examples and corner cases 4 Figure 1: A user interactively synthesizes a regular expression (regex) that accepts phone numbers starting with an optional '+'. After 1) adding some positive and negative examples, the user 2) marks the + sign as literal and the following numbers as a general class of digits to specify how individual characters should be treated by the synthesizer. To refine the synthesis result, the user can either 3) directly mark subexpressions as desired or undesired in the final regex, or 4) ask for additional examples to validate and enhance her understanding of a regex candidate as well as identify and label counterexamples, therefore adding them to the set of user-provided input-output examples.

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