Check out example codes for "bootstrap Breadcrumb Accessibility". It will help you in understanding the concepts better.

Code Example 1

Since breadcrumbs provide a navigation, it’s a good idea to add a meaningful 
label such as aria-label="breadcrumb" to describe the type of navigation
provided in the <nav> element, as well as applying an aria-current="page"
to the last item of the set to indicate that it represents the current page.

Code Example 2

Indicate the current page’s location within a navigational hierarchy that 
automatically adds separators via CSS.
<nav aria-label="breadcrumb">
  <ol class="breadcrumb">
    <li class="breadcrumb-item active" aria-current="page">Home</li>
  </ol>
</nav>

<nav aria-label="breadcrumb">
  <ol class="breadcrumb">
    <li class="breadcrumb-item"><a href="#">Home</a></li>
    <li class="breadcrumb-item active" aria-current="page">Library</li>
  </ol>
</nav>

<nav aria-label="breadcrumb">
  <ol class="breadcrumb">
    <li class="breadcrumb-item"><a href="#">Home</a></li>
    <li class="breadcrumb-item"><a href="#">Library</a></li>
    <li class="breadcrumb-item active" aria-current="page">Data</li>
  </ol>
</nav>

Code Example 3

<nav aria-label="breadcrumb">
  <ol class="breadcrumb">
    <li class="breadcrumb-item"><a href="#">Home</a></li>
    <li class="breadcrumb-item"><a href="#">Library</a></li>
    <li class="breadcrumb-item active">Data</li>
  </ol>
</nav>

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