How does Bootstrap add "/" to breadcrumb components?

Question

Bootstrap breadcrumb components in both v3 and v4 add a "/" to list items:

http://getbootstrap.com/components/#breadcrumbs

https://v4-alpha.getbootstrap.com/components/breadcrumb/

The docs say:

Separators are automatically added in CSS through ::before and content.

So, I looked at the source code, the relevant section showing:

.breadcrumb-item + .breadcrumb-item::before {
  display: inline-block;
  padding-right: 0.5rem;
  padding-left: 0.5rem;
  color: #636c72;
  content: "/";
}

However, the content: "/"; only exists on the breadcrumb-item rule. Yet, it seems to work when I follow the v3 docs, which don't require a breadcrumb-item class for items inside a list:

<ol class="breadcrumb">
  <li class=''><a href="#">Home</a></li>
  <li class=''><a href="#">Library</a></li>
  <li class="active">Data</li>
</ol>

JSFiddle

Why does the above HTML with the above CSS result in / separators being added to items in a .breadcrumb list even though they don't have the .breadcrumb-item class and thus can't benefit from the content: "/" rule? Inspecting the output HTML in JSFiddle shows that no bootstrap javascript magic has added a .breadcrumb-item class to my html list items.

Answer 1

link to this style at github (bootstrap v3.3.7):

https://github.com/twbs/bootstrap/blob/v3.3.7/less/breadcrumbs.less

for (bootstrap v4.0.0):

https://github.com/twbs/bootstrap/blob/v4.0.0-alpha.6/scss/_breadcrumb.scss

(bootstrap v3.3.7 --> breadcrumbs.less)

//
// Breadcrumbs
// --------------------------------------------------


.breadcrumb {
  padding: @breadcrumb-padding-vertical @breadcrumb-padding-horizontal;
  margin-bottom: @line-height-computed;
  list-style: none;
  background-color: @breadcrumb-bg;
  border-radius: @border-radius-base;

  > li {
    display: inline-block;

    + li:before {
      content: "@{breadcrumb-separator}\00a0"; // Unicode space added since inline-block means non-collapsing white-space
      padding: 0 5px;
      color: @breadcrumb-color;
    }
  }

  > .active {
    color: @breadcrumb-active-color;
  }
}

(bootstrap v4.0.0 --> _breadcrumb.scss)

.breadcrumb {
  padding: $breadcrumb-padding-y $breadcrumb-padding-x;
  margin-bottom: $spacer-y;
  list-style: none;
  background-color: $breadcrumb-bg;
  @include border-radius($border-radius);
  @include clearfix;
}

.breadcrumb-item {
  float: left;

  // The separator between breadcrumbs (by default, a forward-slash: "/")
  + .breadcrumb-item::before {
    display: inline-block; // Suppress underlining of the separator in modern browsers
    padding-right: $breadcrumb-item-padding;
    padding-left: $breadcrumb-item-padding;
    color: $breadcrumb-divider-color;
    content: "#{$breadcrumb-divider}";
  }

  // IE9-11 hack to properly handle hyperlink underlines for breadcrumbs built
  // without `<ul>`s. The `::before` pseudo-element generates an element
  // *within* the .breadcrumb-item and thereby inherits the `text-decoration`.
  //
  // To trick IE into suppressing the underline, we give the pseudo-element an
  // underline and then immediately remove it.
  + .breadcrumb-item:hover::before {
    text-decoration: underline;
  }
  + .breadcrumb-item:hover::before {
    text-decoration: none;
  }

  &.active {
    color: $breadcrumb-active-color;
  }
}

Answer 2

In version 3 of Bootstrap, the separators are coming from:

.breadcrumb>li+li:before {
  padding: 0 5px;
  color: #ccc;
  content: "/\00a0";
}

on line 6 of the included file breadcrumbs.less.

Hope this helps! :)