Scroll down to, **and a little bit past**, a desired spot in a UITextView - ios

Question

What I have:
Working code that scrolls to and highlights the next instance of a search term in a UITextView that contains a moderately lengthy document.
What I want:
Instead of scrolling to the desired term so that it is at the very bottom of the TextView, I'd like to scroll slightly PAST the term so that it is better visible in the view.
Where I'm stuck:
I'm weak on how Swift generally & Swift 4 in particular work with Range, and NSRange, so while I suspect that the answer will include capturing some amount of the document beyond the search term itself (say, the lesser of the next 200 characters or the next 5 line breaks), I'm not clear how to accomplish that. Or if there is a better approach to scroll the view a bit more.
Code #1 -- does the highlighting and finds "this" instance of the search term:
func attributedTextHighlighting(instanceNbr: Int, searchTerm: String, inRawHaystackText: String) -> NSMutableAttributedString {
let desiredFont = UIFont(name: "Menlo-Regular", size: self.currentDisplayFontSize)
let fontAttribute : [NSAttributedStringKey : Any] = [NSAttributedStringKey.font: desiredFont as Any]
let attributed = NSMutableAttributedString(string: inRawHaystackText, attributes: fontAttribute)
if !searchTerm.isEmpty {
do {
let foo = NSRegularExpression.escapedPattern(for: searchTerm)
let regex = try NSRegularExpression(pattern: foo, options: .caseInsensitive)
var countingMatches = 0
for match in regex.matches(in: inRawHaystackText, range: NSRange(location: 0, length:
inRawHaystackText.utf16.count)) as [NSTextCheckingResult] {
if countingMatches == instanceNbr {
// highlight this term green
attributed.addAttribute(NSAttributedStringKey.backgroundColor, value: UIColor.green, range: match.range)
theGreenMatchingRange = match.range
} else {
// highlight this term yellow
attributed.addAttribute(NSAttributedStringKey.backgroundColor, value: UIColor.yellow, range: match.range)
}
// and either way, increment the countingMatches
countingMatches += 1
}
} catch {
fatalError("Bad RegEx! \(error)")
}
} else {
print("ofSearchTerm.isEmpty = true")
}
return attributed
}
This code finds the search term in the source text & generates attributed text that highlights the term green (for the current "find") or yellow (for all others). This code works OK.
Code #2 -- scrolls to the next instance of the search term
func scrollToNextMatchButtonTapped() {
print("scrollToNextMatchButtonTapped")
currentlyHighlightedInstance += 1
if currentlyHighlightedInstance == numberOfInstances {
currentlyHighlightedInstance = 0 // since numberOfInstances is 1-based but currentlyHighlightedInstance is 0-based
}
reloadAttribTextWithHighlighting() // calls the above code, so the green highlight moves to the next found instance
textDisplay.scrollRangeToVisible(theGreenMatchingRange) // would really like to scroll to here plus a few lines (not past the end of the document, obviously)
The last line there works (theGreenMatchingRange is the global variable that's set in Code #1 above to be the range of "this" instance of the search term), but it scrolls so that the green-highlighted term is at the very bottom of the window.
What do I need to add or do differently so that the green term isn't at the very bottom?