Finish and clarify comment.

Author: dmsnell

src/wp-includes/html-api/class-wp-html-attribute-token.php

@@ -60,7 +60,11 @@ class WP_HTML_Attribute_Token {
 	 * Byte length of text spanning the attribute inside a tag.
 	 *
 	 * This span starts at the first character of the attribute name
-	 * and it ends
+	 * and it ends after one of three cases:
+	 *
+	 *  - at the end of the attribute name for boolean attributes.
+	 *  - at the end of the value for unquoted attributes.
+	 *  - at the final single or double quote for quoted attributes.
 	 *
 	 * Example:
 	 *