[PSR-7] Errata: scheme delimiters

A [discussion on the mailing list](https://groups.google.com/d/msgid/php-fig/db3d5421-30a5-4135-9f9e-fe432f03d719%40googlegroups.com?utm_medium=email&utm_source=footer) raised the point that
`:` is the actual scheme delimiter. In reviewing [RFC 3986 section 3](https://tools.ietf.org/html/rfc3986#section-3),
I noted that `:` is the end delimiter for a scheme, and `//` is the opening
delimiter for the authority. Since the `UriInterface` does not allow setting the
authority in a single go, the only time the `//` delimiter will likely be used
is as part of the scheme, making the current wording valid. However, the wording
should also note that a trailing `:` delimiter MUST be removed as well.

Created an "Errata" section that adds this; we can vote on it post-acceptance.

proposed/http-message-meta.md

@@ -618,3 +618,26 @@ used to populate the headers of an HTTP message.
 * Phil Sturgeon
 * Chris Wilkinson
 * Evert Pot
+
+## 7. Votes
+
+## 8. Errata
+
+### 8.1 Scheme Delimiters
+
+Per [RFC 3986 section 3](https://tools.ietf.org/html/rfc3986#section-3), `:` is
+considered a closing delimiter for a scheme, and `//` is considered an
+opening delimeter for the URI authority.
+
+In the specification as accepted, `Psr\Http\Message\UriInterface` indicates that
+the methods `withScheme()` and `getScheme()` should ignore a trailing `://`
+delimiter for purposes of consistency. (No similar stipulation is placed on the
+authority, as authority is not treated as a single segment, but rather as its
+own individual segments (`user-info`, `host`, and `port`)).
+
+The `://` delimiter was called out specifically, as schemes are widely either
+presented as the bare-word (e.g., `http`, `https`) or with that delimiter (e.g.,
+`http://`, `https://`), which is the combination of the scheme closing delimiter
+and the authority opening delimiter. However, implementations of the methods
+MUST also strip a closing `:` delimiter when presented without the opening `//`
+delimiter.

proposed/http-message.md

@@ -1165,6 +1165,8 @@ interface UriInterface
      *
      * The string returned MUST omit the trailing "://" delimiter if present.
      *
+     * @see https://github.com/php-fig/fig-standards/blob/proposed/http-message-meta.md#81-scheme-delimiters
+     *     which indicates ":" delimiters must also be omitted.
      * @return string The scheme of the URI.
      */
     public function getScheme();
@@ -1276,6 +1278,8 @@ interface UriInterface
      *
      * An empty scheme is equivalent to removing the scheme.
      *
+     * @see https://github.com/php-fig/fig-standards/blob/proposed/http-message-meta.md#81-scheme-delimiters
+     *     which indicates ":" delimiters must also be omitted.
      * @param string $scheme The scheme to use with the new instance.
      * @return self A new instance with the specified scheme.
      * @throws \InvalidArgumentException for invalid or unsupported schemes.