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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.

Thank you!

it's not currently configurable, but I agree that the highlighting should be more like that. Filed an issue to track it: https://github.com/Kodowa/Light-Table-Playground/issues/277

"I've found this technique gives inferior results to whatever SublimeText is doing."

Oh boy this one we're going to hear for a long time ain't we!?