diff --git a/core/lib/Drupal/Core/Url.php b/core/lib/Drupal/Core/Url.php
index 5bfba84..7525374 100644
--- a/core/lib/Drupal/Core/Url.php
+++ b/core/lib/Drupal/Core/Url.php
@@ -312,10 +312,12 @@ public static function fromRouteMatch(RouteMatchInterface $route_match) {
    *  another application placed within the Drupal site installation.
    *
    * Do not use this method for URLs that have a Drupal route (pages generated
-   * by Drupal). See the documentation of Url::SCHEME_BASE for details.
+   * by Drupal) or for host-relative paths. See the documentation of
+   * Url::SCHEME_BASE for details.
    *
    * @param string $path
-   *   The base-relative path, for example 'robots.txt'.
+   *   The base-relative path, for example 'robots.txt'. Leading slashes are
+   *   discarded.
    * @param array $options
    *   (optional) An array of options. See Url::fromUri() for details.
    *
@@ -329,6 +331,8 @@ public static function fromRouteMatch(RouteMatchInterface $route_match) {
    * @see \Drupal\Core\Url::fromRoute()
    */
   public static function fromBaseRelativePath($path, $options = array()) {
+    // Trim leading slashes to ensure a base-relative path is used.
+    $path = static::trimLeadingSlashes($path);
     return static::fromUri(static::SCHEME_BASE . ':' . $path, $options);
   }
 
@@ -336,15 +340,17 @@ public static function fromBaseRelativePath($path, $options = array()) {
    * Creates a new Url object from an unrouted, host-relative path.
    *
    * This method should only be used for paths within the same host as the
-   * site installation.
+   * site installation that do not have a Drupal route and are not within the
+   * Drupal installation directory.
    *
    * Do not use this method for URLs that have a Drupal route (pages generated
-   * by Drupal). See the documentation of Url::SCHEME_BASE for details.
+   * by Drupal) or for base-relative paths. See the documentation of
+   * Url::SCHEME_BASE for details.
    *
    * @param string $path
    *   The host-relative path. For example, if Drupal is installed in the
    *   subdirectory http://example.com/drupal/, use 'index.html' for a URL to
-   *   http://example.com/index.html.
+   *   http://example.com/index.html. Leading slashes are discarded.
    * @param array $options
    *   (optional) An array of options. See Url::fromUri() for details.
    *
@@ -358,18 +364,65 @@ public static function fromBaseRelativePath($path, $options = array()) {
    * @see \Drupal\Core\Url::fromRoute()
    */
   public static function fromHostRelativePath($path, $options = array()) {
+    // Trim leading slashes, then add exactly one, to ensure a host-relative
+    // path is used.
+    $path = static::trimLeadingSlashes($path);
     return static::fromUri(static::SCHEME_BASE . ':/' . $path, $options);
   }
 
   /**
+   * Trims leading slashes from a path.
+   *
+   * @param string $path
+   *   A potential base-relative or host-relative path.
+   *
+   * @return string
+   *   The path, with leading slashes trimmed.
+   */
+  protected static function trimLeadingSlashes($path) {
+    return preg_replace('/^(\/)+/', '', $path);
+  }
+
+  /**
+   * Creates a Url object for a path from user input.
+   *
+   * Use this method to create a URL for paths from user input that may or may
+   * not correspond to a valid Drupal route.
+   *
+   * @param string $path
+   *   A path string from user input. Only three types of paths are allowed:
+   *   - Site paths, beginning with a '/'.
+   *   - Query strings, beginning with a '?'.
+   *   - Fragments, beginning with a '#'.
+   * @param array $options
+   *   (optional) An array of options. See Url::fromUri() for details.
+   *
+   * @return \Drupal\Core\Url
+   *   A new Url object based on user input.
+   *
+   * @todo The intent here is to support a user interaction pattern where
+   *   entering one of the three allowed characters at the beginning of a
+   *   field denotes that the user wants to link to a specific path on the
+   *   site, with all other input interpreted as an attempt to autocomplete the
+   *   label of a specific resource. How do we document that, and how do we
+   *   establish the expectation for other APIs and for UIs?
+   */
+  public static function fromUserInput($path, $options = []) {
+    if ((strpos($path, '/') !== 0) && (strpos($path, '/') !== 0) && (strpos($path, '/') !== 0)) {
+      throw new \InvalidArgumentException(String::format('The path @path is not valid as user input. User-input paths must begin with one of the following characters: / # ?', ['@path' => $path]));
+    }
+    return static::fromUri(static::SCHEME_USER_PATH . ':' . $path, $options);
+  }
+
+  /**
    * Creates a new Url object from a URI.
    *
    * This method is used to create URLs for internal and external URIs with a
    * unified API and storage format.
    *
-   * - For URIs that have Drupal routes (that is, most pages generated by
-   *   Drupal), use Url::fromRoute() whenever possible, to avoid circumventing
-   *   the routing system.
+   * - For URIs that have Drupal routes (pages generated by Drupal), use
+   *   Url::fromRoute() whenever possible, to avoid circumventing the routing
+   *   system.
    * - For paths from user input that may or may not correspond to a valid
    *   Drupal route, use Url::fromUserInput().
    * - For base-relative and host-relative paths that are not created by Drupal,