type urlFrag struct {
	url, frag string
}

var (
	mu          sync.Mutex
	crawled     = make(map[string]bool)      // URL without fragment -> true
	neededFrags = make(map[urlFrag][]string) // URL#frag -> who needs it
)

var aRx = regexp.MustCompile(`<a href=['"]?(/[^\s'">]+)`)

// Owned by crawlLoop goroutine:
var (
	linkSources = make(map[string][]string) // url no fragment -> sources

    validations:
      required: true

  - type: textarea
    id: proposal
    attributes:
      label: "Proposal"
      description: "What is the proposed change? Who does this proposal help, and why? Please describe as precisely as possible the change to the language."
    validations:
      required: true

  - type: textarea
    id: language-spec-changes
    attributes:

call site.
</p>

<p>
Given the function and calls
</p>
<pre>
func Greeting(prefix string, who ...string)
Greeting("nobody")
Greeting("hello:", "Joe", "Anna", "Eileen")
</pre>

<p>
within <code>Greeting</code>, <code>who</code> will have the value
<code>nil</code> in the first call, and
<code>[]string{"Joe", "Anna", "Eileen"}</code> in the second.
</p>

call site.
</p>

<p>
Given the function and calls
</p>
<pre>
func Greeting(prefix string, who ...string)
Greeting("nobody")
Greeting("hello:", "Joe", "Anna", "Eileen")
</pre>

<p>
within <code>Greeting</code>, <code>who</code> will have the value
<code>nil</code> in the first call, and
<code>[]string{"Joe", "Anna", "Eileen"}</code> in the second.
</p>