Require that metrics be grouped together for text format.

While it'd be nice for TYPE to be first,
that's not what the examples do so we leave the ordering
of HELP/TYPE unspecified.

content/docs/instrumenting/exposition_formats.md

@@ -72,7 +72,7 @@ metric name, and the second is either `counter`, `gauge`, `histogram`,
 one `TYPE` line may exist for the same metric name. The `TYPE` line for a
 metric name has to appear before the first sample is reported for that metric
 name. If there is no `TYPE` line for a metric name, the type is set to
-`untyped`.  Remaining lines describe samples, one per line, with the following
+`untyped`. Remaining lines describe samples, one per line, with the following
 syntax (EBNF):
 
     metric_name [
@@ -82,6 +82,9 @@ syntax (EBNF):
 `metric_name` and `label_name` have the usual Prometheus expression language restrictions. `label_value` can be any sequence of UTF-8 characters, but the backslash, the double-quote, and the line-feed characters have to be escaped as `\\`, `\"`, and `\n`, respectively.
 `value` is a float, and timestamp an `int64` (milliseconds since epoch, i.e. 1970-01-01 00:00:00 UTC, excluding leap seconds), represented as required by the [Go strconv package](http://golang.org/pkg/strconv/) (see functions `ParseInt` and `ParseFloat`). In particular, `Nan`, `+Inf`, and `-Inf` are valid values.
 
+All lines for a given metric should be provided as one uninterrupted group, with
+the optional `HELP` and `TYPE` lines first.
+
 The `histogram` and `summary` types are difficult to represent in the text
 format. The following conventions apply: