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[MUSIC]

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So far, we've built a single
parent with a single child.

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This child was able to share and
override the functionality of the parent,

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allowing us to reduce the amount
of repetition in our code.

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But we don't need to stop there.

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We can create as many children as we want,
and each of these children will inherit

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all of the abilities and
attributes of the parent class.

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However, they will not have
any of the added abilities and

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features of the other children.

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This is called a Sibling Relationship,
because both classes have the same parent.

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You could of course add the same
features to another child,

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but there's a better way.

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When you want to create a new class
that has all the abilities and

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attributes of a child,
as well as the parent,

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child classes can be extended
further to create grandchildren.

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You may continue to add children for
an infinite number of generations.

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Each subsequent generation
gaining the attributes and

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actions of all generations before.

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The only limitation is that you may
only extend from one parent at a time.

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Let's go back to our code and
see this in action.

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Let's create a second
child of ListingBasic.

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We'll call this ListingInactive.

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And we'll extend, ListingBasic.

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This will be a sibling of ListingPremium.

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Without adding any code, this class will
have all the abilities and attributes of

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ListingBasic, and can be swapped out for
that parent class just like we did before.

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However, this class will not know
about the description feature, so

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we will not be able to
use that functionality.

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Let's include this new
class in our config,

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Now we can switch out our test
object to use the ListingInactive.

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Open index.php.

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Now let's preview this in a browser.

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Because we're passing
the description into our construct,

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it just ignores the description,
because ListingInactive does not use that.

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Let's go back and create another class.

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This one will be a child
of ListingPremium.

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We'll call this ListingFeatured,

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And it extends ListingPremium.

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This class will inherit
all the abilities and

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attributes of not only the ListingPremium,
but also the ListingBasic.

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Once more, we need to include
this class in our config.

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Now we can add another test.

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Now let's preview in the browser.

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Let's view the page source and
increase the font size.

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Even though ListingFeatured doesn't
have the set description methods or

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attributes defined, it is using
the inherited behaviors and attributes.