<div id="m1">
  <a href="#">내용1_1</a><span>내용1_2</span>
</div>
<div id="m2">
  <div>
    <a href="#">내용2_1</a><span>내용2_2</span>
  </div>
</div>
<div id="m3">
  <div><span>내용3_1</span></div>
</div>
<div id="m4">
  <span class="m">내용4_1</span><span>내용4_2</span><span>내용4_3</span><em>내용4_4</em>
</div>
<div id="m5">
  <span class="m">내용5_1</span><span>내용5_2</span><span>내용5_3</span>
</div>
<div id="m6">
  <div><span>내용6_1</span></div>
  <div>내용6_2</div>
</div>

* {
  margin: 5px;
}

$(document).ready(function() {
  $("#m1").children().css("border", "2px solid red");
  $("#m2").children().children("span").css("border", "2px solid orange");
  $("#m3 span").closest("div").css("border", "2px solid yellow");
  $("#m4 > span.m").nextUntil("em").css("border", "2px solid green");
  $("#m5 > span").filter(".m").css("border", "2px solid blue");
  $("#m6 > div").has("span").css("border", "2px solid navy");
});