<iframe src="https://amazon.com">sorry</iframe>

<iframe>

some_folder

sudo rm -r some_folder/

-r

case-sensitive

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<student>
   <name>George</name>
   <city>Tbilisi</city>
   <phone>(011) 123-4567</phone>
   <address>Wrong syntax</ADdress>
   <hr />
</student>

error on line 6 at column 23: Opening and ending tag mismatch: address line 0 and ADdress

in an appropriate order

<outer_element>
   <internal_element>
      Right, because the inner tag is closed before the outer
   </internal_element>
</outer_element>

npm install

npm install -h

npm install --help

.alert {
  // The parent selector can be used to add pseudo-classes to the outer
  // selector.
  &:hover {
    font-weight: bold;
  }

  // It can also be used to style the outer selector in a certain context, such
  // as a body set to use a right-to-left language.
  [dir=rtl] & {
    margin-left: 0;
    margin-right: 10px;
  }

  // You can even use it as an argument to pseudo-class selectors.
  :not(&) {
    opacity: 0.8;
  }
}

.alert:hover {
  font-weight: bold;
}
[dir=rtl] .alert {
  margin-left: 0;
  margin-right: 10px;
}
:not(.alert) {
  opacity: 0.8;
}

.btn-a {
    display: inline-block;
    padding: 10px;
}
.btn-b {
    @extend .btn-a;
    background-color: black;
}

.btn-a, .btn-b {
    display: inline-block;
    padding: 10px;
}
.btn-b {
    background-color: black;
}

abstract class Fruit { 
    private $color; 
    
    abstract public function eat(); 
    
    public function setColor($c) { 
        $this->color = $c; 
    } 
} 

class Apple extends Fruit {
    public function eat() {
        echo "Omnomnom";
    }
}

$obj = new Apple();
$obj->eat();

interface

letter-spacing

word-spacing

h1 {
    letter-spacing: 2px;
    word-spacing: 10px;
}

<div class="container">
  <div class="row">
    <div class="col-sm">col-sm</div>
    <div class="col-sm">col-sm</div>
    <div class="col-sm">col-sm</div>
  </div>
</div>

100%

540px

720px

960px

1140px