Another example from Hunt and McIlroy,
“An Algorithm for Differential File Comparison.”
https://www.cs.dartmouth.edu/~doug/diff.pdf

Anchored diff gives up on finding anything,
since there are no unique lines.

-- old --
a
b
c
a
b
b
a
-- new --
c
a
b
a
b
c
-- diff --
diff old new
--- old
+++ new
@@ -1,7 +1,6 @@
-a
-b
-c
-a
-b
-b
-a
+c
+a
+b
+a
+b

// capture wraps the expression in a capturing group.
func capture(res ...*regexp.Regexp) *regexp.Regexp {
	return match(`(` + expression(res...).String() + `)`)
}

// anchored anchors the regular expression by adding start and end delimiters.
func anchored(res ...*regexp.Regexp) *regexp.Regexp {
	return match(`^` + expression(res...).String() + `$`)
}

// ValidatorFunc validates a value.

// smallest number of “unique” lines inserted and removed,
// where unique means a line that appears just once in both old and new.
// We call this an “anchored diff” because the unique lines anchor
// the chosen matching regions. An anchored diff is usually clearer
// than a standard diff, because the algorithm does not try to
// reuse unrelated blank lines or closing braces.

	if startCond == ^syntax.EmptyOp(0) { // impossible
		return nil
	}
	if startCond&syntax.EmptyBeginText != 0 && pos != 0 {
		// Anchored match, past beginning of text.
		return nil
	}

	b := newBitState()
	i, end := b.inputs.init(nil, ib, is)
	b.reset(re.prog, end, ncap)

	// Anchored search must start at the beginning of the input
	if startCond&syntax.EmptyBeginText != 0 {
		if len(b.cap) > 0 {
			b.cap[0] = pos

		if len(result) == 0 {
			result = nil
		}
		return
	}

	// regexp has a non-empty literal prefix; Lookup(lit) computes
	// the indices of possible complete matches; use these as starting
	// points for anchored searches
	// (regexp "^" matches beginning of input, not beginning of line)
	r = regexp.MustCompile("^" + r.String()) // compiles because r compiled

	// same comment about Lookup applies here as in the loop above

		}
	}
	if l.Recv != "" {
		return "#" + l.Recv + "." + l.Name
	}
	return "#" + l.Name
}

// DefaultID returns the default anchor ID for the heading h.
//
// The default anchor ID is constructed by converting every
// rune that is not alphanumeric ASCII to an underscore
// and then adding the prefix “hdr-”.
// For example, if the heading text is “Go Doc Comments”,

	var flag lazyFlag
	if pos == 0 {
		flag = newLazyFlag(-1, r)
	} else {
		flag = i.context(pos)
	}
	for {
		if len(runq.dense) == 0 {
			if startCond&syntax.EmptyBeginText != 0 && pos != 0 {
				// Anchored match, past beginning of text.
				break
			}
			if m.matched {
				// Have match; finished exploring alternatives.
				break
			}
			if len(m.re.prefix) > 0 && r1 != m.re.prefixRune && i.canCheckPrefix() {

// be true is: at any InstAlt, there must be no ambiguity about what branch to  take.
func compileOnePass(prog *syntax.Prog) (p *onePassProg) {
	if prog.Start == 0 {
		return nil
	}
	// onepass regexp is anchored
	if prog.Inst[prog.Start].Op != syntax.InstEmptyWidth ||
		syntax.EmptyOp(prog.Inst[prog.Start].Arg)&syntax.EmptyBeginText != syntax.EmptyBeginText {
		return nil
	}

        def tab = findTab('Tests')
        def anchor = tab.select("TD").find { it.text() == testName }
        return anchor?.parent()
    }

    private def findAllTestDetails(String testName) {
        def tab = findTab('Tests')
        def anchors = tab.select("TD").findAll { it.text() == testName }
        return anchors.collect { it?.parent() }
    }

            }
        }
    }

    private void addAnchorsForHeadings(Document document) {
        // add anchors for all of the headings
        for (Element heading : document.body().select("h2,h3,h4")) {
            String anchorName = heading.text().toLowerCase().replaceAll(" ", "-");
            heading.attr("id", anchorName);
        }
    }