Bootstrap: Multiple nested rows within row?

Question

I know you can nest rows within nested columns, but is it 'against the rules' to nest rows directly within rows?

eg:

<div class="row">

  <div class="row">
     cols in here
  </div>

  <div class="row">
     cols in here
  </div>

  <div class="row">
     cols in here
  </div>

</div>

Or must these always be within columns?

Answer 1

is it 'against the rules' to nest rows directly within rows?

Not against the rules as such, but not a best practice as per the guidelines.

Per bootstrap guidelines, third point under introduction -

..and only columns may be immediate children of rows".

*_{Edit: This is still true with Bootstrap 4.0 Beta. The link to the docs above will automatically redirect to the version 3.3 documentation. Thank you @Aakash for pointing this out.}

This is because of the padding which Bootstrap uses for its layout, it is a good practice to nest via row-column-row pattern i.e. nest a row with one column across to nest.

See the difference in the snippet below. The first set of markup breaks the Bootstrap layout, although nothing bad happens.

<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css" rel="stylesheet"/>
<div class="container">
  <div class="row">
    <div class="row">
      <div class="col-xs-6">One</div>
      <div class="col-xs-6">Two</div>
    </div>
  </div>
</div>
<hr>
<div class="container">
  <div class="row">
    <div class="col-xs-12">
      <div class="row">
        <div class="col-xs-6">One</div>
        <div class="col-xs-6">Two</div>
      </div>
    </div>
  </div>
</div>
<hr>
<div class="container">
  <div class="row">
    <div class="col-xs-12">One</div>
    <div class="col-xs-12">Two</div>
    <div class="col-xs-12">Three</div>
  </div>
</div>