Turn slashes into .*?(/).*? and leave the rest alone? If you don't want to treat slashes specially and want to allow "ab" to match "aqqqb" then I don't t

Turn slashes into .*?(/).*? and leave the rest alone? If you don't want to treat slashes specially and want to allow "ab" to match "aqqqb" then I don't think you can do it without creating a giant regex. You can go for a modified longest common subsequence algorithm. Edit: here's how you can do it: // gives one point for each letter matched // plus an extra point if the next letter is also a match let rec scorematch = function | true::true::r -> 2 + scorematch (true::r) | true::r -> 1 + scorematch r | false::r -> scorematch r | [] -> 0 // find the match with best score let rec search xs ys = match (xs,ys) with | (x::xr, y::yr) -> let matches = [false::search xr ys; false::search xs yr] let matches = if x=y then (true::search xr yr)::matches else matches matches |> List.maxBy scorematch | _,ys -> List.map (fun _ -> false) ys let underline xs ys = search (List.ofSeq xs) (List.ofSeq ys) |> List.map (fun b -> if b then "-" else " ") |> String.Concat for x in ["foobarbaz"; "foobaXrbaz"; "foobXaXrbaz"; "foobXaXrbazr"] do Console.WriteLine x Console.WriteLine (underline "bar" x) For search term "bar" this outputs: foobarbaz --- foobaXrbaz -- - foobXaXrbaz - - - foobXaXrbazr -- - You'll want to memoize this or apply dynamic programming.