Index: wp-includes/general-template.php
===================================================================
--- wp-includes/general-template.php	(revision 41378)
+++ wp-includes/general-template.php	(working copy)
@@ -362,27 +362,32 @@
  * The login format HTML is echoed by default. Pass a false value for `$echo` to return it instead.
  *
  * @since 3.0.0
+ * @since 2.8.0 $placeholder_username and placeholder_password arguments added.
  *
  * @param array $args {
  *     Optional. Array of options to control the form output. Default empty array.
  *
- *     @type bool   $echo           Whether to display the login form or return the form HTML code.
- *                                  Default true (echo).
- *     @type string $redirect       URL to redirect to. Must be absolute, as in "https://example.com/mypage/".
- *                                  Default is to redirect back to the request URI.
- *     @type string $form_id        ID attribute value for the form. Default 'loginform'.
- *     @type string $label_username Label for the username or email address field. Default 'Username or Email Address'.
- *     @type string $label_password Label for the password field. Default 'Password'.
- *     @type string $label_remember Label for the remember field. Default 'Remember Me'.
- *     @type string $label_log_in   Label for the submit button. Default 'Log In'.
- *     @type string $id_username    ID attribute value for the username field. Default 'user_login'.
- *     @type string $id_password    ID attribute value for the password field. Default 'user_pass'.
- *     @type string $id_remember    ID attribute value for the remember field. Default 'rememberme'.
- *     @type string $id_submit      ID attribute value for the submit button. Default 'wp-submit'.
- *     @type bool   $remember       Whether to display the "rememberme" checkbox in the form.
- *     @type string $value_username Default value for the username field. Default empty.
- *     @type bool   $value_remember Whether the "Remember Me" checkbox should be checked by default.
- *                                  Default false (unchecked).
+ *     @type bool   $echo                 Whether to display the login form or return the form HTML code.
+ *                                        Default true (echo).
+ *     @type string $redirect             URL to redirect to. Must be absolute, as in
+ *                                        "https://example.com/mypage/". Default is to redirect back to the
+ *                                        request URI.
+ *     @type string $form_id              ID attribute value for the form. Default 'loginform'.
+ *     @type string $label_username       Label for the username or email address field. Default
+ *                                        'Username or Email Address'.
+ *     @type string $label_password       Label for the password field. Default 'Password'.
+ *     @type string $label_remember       Label for the remember field. Default 'Remember Me'.
+ *     @type string $label_log_in         Label for the submit button. Default 'Log In'.
+ *     @type string $id_username          ID attribute value for the username field. Default 'user_login'.
+ *     @type string $id_password          ID attribute value for the password field. Default 'user_pass'.
+ *     @type string $id_remember          ID attribute value for the remember field. Default 'rememberme'.
+ *     @type string $id_submit            ID attribute value for the submit button. Default 'wp-submit'.
+ *     @type string $placeholder_username Placeholder attribute value for the username field. Default empty.
+ *     @type string $placeholder_password Placeholder attribute value for the password field. Default empty.
+ *     @type bool   $remember             Whether to display the "rememberme" checkbox in the form.
+ *     @type string $value_username       Default value for the username field. Default empty.
+ *     @type bool   $value_remember       Whether the "Remember Me" checkbox should be checked by default.
+ *                                        Default false (unchecked).
  *
  * }
  * @return string|void String when retrieving.
@@ -401,6 +406,8 @@
 		'id_password' => 'user_pass',
 		'id_remember' => 'rememberme',
 		'id_submit' => 'wp-submit',
+		'placeholder_username' => '',
+		'placeholder_password' => '',
 		'remember' => true,
 		'value_username' => '',
 		// Set 'value_remember' to true to default the "Remember me" checkbox to checked.
@@ -460,11 +467,11 @@
 			' . $login_form_top . '
 			<p class="login-username">
 				<label for="' . esc_attr( $args['id_username'] ) . '">' . esc_html( $args['label_username'] ) . '</label>
-				<input type="text" name="log" id="' . esc_attr( $args['id_username'] ) . '" class="input" value="' . esc_attr( $args['value_username'] ) . '" size="20" />
+				<input type="text" name="log" id="' . esc_attr( $args['id_username'] ) . '" class="input" placeholder="' . esc_attr( $args['placeholder_username'] ) . '" value="' . esc_attr( $args['value_username'] ) . '" size="20" />
 			</p>
 			<p class="login-password">
 				<label for="' . esc_attr( $args['id_password'] ) . '">' . esc_html( $args['label_password'] ) . '</label>
-				<input type="password" name="pwd" id="' . esc_attr( $args['id_password'] ) . '" class="input" value="" size="20" />
+				<input type="password" name="pwd" id="' . esc_attr( $args['id_password'] ) . '" class="input" placeholder="' . esc_attr( $args['placeholder_password'] ) . '" value="" size="20" />
 			</p>
 			' . $login_form_middle . '
 			' . ( $args['remember'] ? '<p class="login-remember"><label><input name="rememberme" type="checkbox" id="' . esc_attr( $args['id_remember'] ) . '" value="forever"' . ( $args['value_remember'] ? ' checked="checked"' : '' ) . ' /> ' . esc_html( $args['label_remember'] ) . '</label></p>' : '' ) . '