When I embed a tweet like this:

I wish people would stop using u- as a prefix for utility classes in CSS. Use util- instead. You're messing with my microformats.

— Kevin Marks (@kevinmarks) February 19, 2016
It generates html like this in an iframe:
Kevin Marks @kevinmarks

I wish people would stop using u- as a prefix for utility classes in CSS. Use util- instead. You're messing with my microformats.

when I parse this to jf2 I get 
{
    "linkBlend": {
        "children": [
            "https://twitter.com/kevinmarks", 
            "https://twitter.com/kevinmarks/status/700752598123433985"
        ]
    }, 
    "updated": "2016-02-19T18:43:33+0000", 
    "name": "Follow\n\n\n\n\n\n\n\n\nKevin Marks\n@kevinmarks\n\n\n\n\nI wish people would stop using u- as a prefix for utility classes in CSS. Use util- instead. You're messing with my microformats.\n\n\n10:43 AM - 19 Feb 2016\n\n\n\n\n\n 1\n1 Retweet\n\n\n 4\n4 likes", 
    "hiddenInNarrowEnv": "\n Follow\n", 
    "hiddenVisually": {
        "children": [
            "1 Retweet", 
            "4 likes"
        ]
    }, 
    "cf": "\n\n\n Follow\n\n\n\n\n\n\n\n\nKevin Marks\n@kevinmarks\n\n\n", 
    "hiddenInWideEnv": "", 
    "url": "https://twitter.com/kevinmarks/status/700752598123433985", 
    "floatRight": "\n\n Follow\n\n\n", 
    "entry-content": "\nI wish people would stop using u- as a prefix for utility classes in CSS. Use util- instead. You're messing with my microformats.\n\n\n10:43 AM - 19 Feb 2016\n\n\n\n\n\n 1\n1 Retweet\n\n\n 4\n4 likes\n\n\n", 
    "entry-title": "I wish people would stop using u- as a prefix for utility classes in CSS. Use util- instead. You're messing with my microformats.", 
    "type": "entry"
}
Note the spurious 'cf', 'linkBlend', 'hiddenInNarrowEnv', 'hiddenVisually', 'hiddenInWideEnv' and 'floatRight' properties from the u- utility classes

Full mf2 version: 

 {
    "rels": {}, 
    "items": [
        {
            "type": [
                "h-entry"
            ], 
            "properties": {
                "linkBlend": [
                    "https://twitter.com/kevinmarks", 
                    "https://twitter.com/kevinmarks/status/700752598123433985"
                ], 
                "updated": [
                    "2016-02-19T18:43:33+0000"
                ], 
                "name": [
                    "Follow\n\n\n\n\n\n\n\n\nKevin Marks\n@kevinmarks\n\n\n\n\nI wish people would stop using u- as a prefix for utility classes in CSS. Use util- instead. You're messing with my microformats.\n\n\n10:43 AM - 19 Feb 2016\n\n\n\n\n\n 1\n1 Retweet\n\n\n 4\n4 likes"
                ], 
                "hiddenInNarrowEnv": [
                    "\n Follow\n"
                ], 
                "hiddenVisually": [
                    "1 Retweet", 
                    "4 likes"
                ], 
                "cf": [
                    "\n\n\n Follow\n\n\n\n\n\n\n\n\nKevin Marks\n@kevinmarks\n\n\n"
                ], 
                "hiddenInWideEnv": [
                    ""
                ], 
                "url": [
                    "https://twitter.com/kevinmarks/status/700752598123433985"
                ], 
                "floatRight": [
                    "\n\n Follow\n\n\n"
                ], 
                "entry-content": [
                    {
                        "html": "\n<p class=\"Tweet-text e-entry-title\" dir=\"ltr\" lang=\"en\">I wish people would stop using u- as a prefix for utility classes in CSS. Use util- instead. You're messing with my microformats.</p>\n<div class=\"Tweet-metadata dateline\">\n<a class=\"u-linkBlend u-url customisable-highlight long-permalink\" data-datetime=\"2016-02-19T18:43:33+0000\" data-scribe=\"element:full_timestamp\" href=\"https://twitter.com/kevinmarks/status/700752598123433985\">\n<time class=\"dt-updated\" datetime=\"2016-02-19T18:43:33+0000\" pubdate=\"\" title=\"Time posted: 19 Feb 2016, 18:43:33 (UTC)\">10:43 AM - 19 Feb 2016</time></a>\n</div>\n<ul aria-label=\"Tweet actions\" class=\"Tweet-actions\" data-scribe=\"component:actions\" role=\"menu\">\n<li class=\"Tweet-action\">\n<a class=\"TweetAction TweetAction--reply web-intent\" data-scribe=\"element:reply\" href=\"https://twitter.com/intent/tweet?in_reply_to=700752598123433985\"><div aria-label=\"Reply\" class=\"Icon Icon--reply TweetAction-icon\" role=\"img\" title=\"Reply\"></div></a></li>\n<li class=\"Tweet-action\">\n<a class=\"TweetAction TweetAction--retweet web-intent\" data-scribe=\"element:retweet\" href=\"https://twitter.com/intent/retweet?tweet_id=700752598123433985\"><div aria-label=\"Retweet\" class=\"Icon Icon--retweet TweetAction-icon\" role=\"img\" title=\"Retweet\"></div> <span aria-hidden=\"true\" class=\"TweetAction-stat\" data-scribe=\"element:retweet_count\">1</span>\n<span class=\"u-hiddenVisually\">1 Retweet</span>\n</a></li>\n<li class=\"Tweet-action\">\n<a class=\"TweetAction TweetAction--heart web-intent\" data-scribe=\"element:heart\" href=\"https://twitter.com/intent/like?tweet_id=700752598123433985\"><div aria-label=\"Like\" class=\"Icon Icon--heart TweetAction-icon\" role=\"img\" title=\"Like\"></div> <span aria-hidden=\"true\" class=\"TweetAction-stat\" data-scribe=\"element:heart_count\">4</span>\n<span class=\"u-hiddenVisually\">4 likes</span>\n</a></li>\n</ul>\n", 
                        "value": "\nI wish people would stop using u- as a prefix for utility classes in CSS. Use util- instead. You're messing with my microformats.\n\n\n10:43 AM - 19 Feb 2016\n\n\n\n\n\n 1\n1 Retweet\n\n\n 4\n4 likes\n\n\n"
                    }
                ], 
                "entry-title": [
                    {
                        "html": "I wish people would stop using u- as a prefix for utility classes in CSS. Use util- instead. You're messing with my microformats.", 
                        "value": "I wish people would stop using u- as a prefix for utility classes in CSS. Use util- instead. You're messing with my microformats."
                    }
                ]
            }
        }
    ], 
    "rel-urls": {}
}
here's the html markup from twitter: 

<div class="EmbeddedTweet js-clickToOpenTarget" data-click-to-open-target="https://twitter.com/kevinmarks/status/700752598123433985" data-iframe-title="Twitter Tweet" data-dt-full="%{hours12}:%{minutes} %{amPm} - %{day} %{month} %{year}" data-dt-months="Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec" data-dt-am="AM" data-dt-pm="PM" data-dt-now="now" data-dt-s="s" data-dt-m="m" data-dt-h="h" data-dt-second="second" data-dt-seconds="seconds" data-dt-minute="minute" data-dt-minutes="minutes" data-dt-hour="hour" data-dt-hours="hours" data-dt-abbr="%{number}%{symbol}" data-dt-short="%{day} %{month}" data-dt-long="%{day} %{month} %{year}" data-scribe="page:tweet" id="twitter-widget-0" lang="en" data-twitter-event-id="0">

    <div class="EmbeddedTweet-tweet">
<blockquote class="Tweet h-entry js-tweetIdInfo subject expanded
                   is-deciderHtmlWhitespace" cite="https://twitter.com/kevinmarks/status/700752598123433985" data-tweet-id="700752598123433985" data-scribe="section:subject">
  <div class="Tweet-header u-cf">
    <div class="Tweet-brand u-floatRight">
      <span class="u-hiddenInNarrowEnv">
<a class="FollowButton follow-button profile" data-scribe="component:followbutton" href="https://twitter.com/kevinmarks" role="button" title="Follow Kevin Marks on Twitter"><span class="FollowButton-bird"><div class="Icon Icon--twitter " aria-label="" title="" role="presentation"></div></span> Follow</a>
</span>
      <span class="u-hiddenInWideEnv"><a href="https://twitter.com/download" data-scribe="element:logo"><div class="Icon Icon--twitter " aria-label="Get Twitter app" title="Get Twitter app" role="img"></div></a></span>
    </div>
    
<div class="TweetAuthor" data-scribe="component:author">
  <a class="TweetAuthor-link Identity u-linkBlend" data-scribe="element:user_link" href="https://twitter.com/kevinmarks" aria-label="Kevin Marks (screen name: kevinmarks)">
    <span class="TweetAuthor-avatar Identity-avatar">
      <img class="Avatar" data-scribe="element:avatar" data-src-2x="https://pbs.twimg.com/profile_images/553009683087114240/tU5HkXEI_bigger.jpeg" alt="" data-src-1x="https://pbs.twimg.com/profile_images/553009683087114240/tU5HkXEI_normal.jpeg" src="https://pbs.twimg.com/profile_images/553009683087114240/tU5HkXEI_normal.jpeg">
    </span>
    <span class="TweetAuthor-name Identity-name customisable-highlight" title="Kevin Marks" data-scribe="element:name">Kevin Marks</span>
    
    <span class="TweetAuthor-screenName Identity-screenName" title="@kevinmarks" data-scribe="element:screen_name">@kevinmarks</span>
  </a>
</div>

  </div>

  <div class="Tweet-body e-entry-content" data-scribe="component:tweet">
    <p class="Tweet-text e-entry-title" lang="en" dir="ltr">I wish people would stop using u- as a prefix for utility classes in CSS. Use util- instead. You're messing with my microformats.</p>


    <div class="Tweet-metadata dateline">
      

<a class="u-linkBlend u-url customisable-highlight long-permalink" data-datetime="2016-02-19T18:43:33+0000" data-scribe="element:full_timestamp" href="https://twitter.com/kevinmarks/status/700752598123433985">
<time class="dt-updated" datetime="2016-02-19T18:43:33+0000" pubdate="" title="Time posted: 19 Feb 2016, 18:43:33 (UTC)">10:43 AM - 19 Feb 2016</time></a>
    </div>


    <ul class="Tweet-actions" data-scribe="component:actions" role="menu" aria-label="Tweet actions">
      <li class="Tweet-action">
<a class="TweetAction TweetAction--reply web-intent" href="https://twitter.com/intent/tweet?in_reply_to=700752598123433985" data-scribe="element:reply"><div class="Icon Icon--reply TweetAction-icon" aria-label="Reply" title="Reply" role="img"></div></a></li>
      <li class="Tweet-action">
<a class="TweetAction TweetAction--retweet web-intent" href="https://twitter.com/intent/retweet?tweet_id=700752598123433985" data-scribe="element:retweet"><div class="Icon Icon--retweet TweetAction-icon" aria-label="Retweet" title="Retweet" role="img"></div>    <span class="TweetAction-stat" data-scribe="element:retweet_count" aria-hidden="true">1</span>
    <span class="u-hiddenVisually">1 Retweet</span>
</a></li>
      <li class="Tweet-action">
<a class="TweetAction TweetAction--heart web-intent" href="https://twitter.com/intent/like?tweet_id=700752598123433985" data-scribe="element:heart"><div class="Icon Icon--heart TweetAction-icon" aria-label="Like" title="Like" role="img"></div>    <span class="TweetAction-stat" data-scribe="element:heart_count" aria-hidden="true">4</span>
    <span class="u-hiddenVisually">4 likes</span>
</a></li>
    </ul>
  </div>
</blockquote>
</div>
  </div>