$re = '/<span[^>]*>.*?<\/span>/m';
$str = '<p>Qualifiers are used to adjust qualities of an object or a variable.</p>
<p>There are two types of qualifiers in C++. CV <span style="color: #3665f3;"><strong>Qualifiers</strong></span> and Storage Duration <span style="color: #3665f3;"><strong>Qualifiers</strong></span>. CV stands for constant and volatile.</p>
<p>CV <span style="color: #3665f3;"><strong>Qualifiers</strong></span></p>
<ul>
<li>const - marks a variable as read-only or immutable.</li>
<li>mutable - is used on data members to make them writable from a const qualified member function.</li>
<li>volatile - mark a variable that may be changed by another process. This is partly deprecated in C++ 20.</li>
</ul>
<p>Storage Duration Qualifiers are used to define the duration or lifetime of a variable. By default, a variable defined within a block has an automatic lifetime.</p>
<p>Storage Duration <span style="color: #3665f3;"><strong>Qualifiers</strong></span></p>
<ul>
<li>static - variables defined to have life <span>beyond</span> the execution of a block. Static variables live for the duration of the program. Commonly used for keeping state between usages between a given function or a method. By default a variable defined outside of any block is static.</li>
<li>register - are variables stored in processor registers. This can make them faster <span style="color: #3665f3;"><strong>Qualifiers</strong></span> and more efficient. This qualifier is taken by the compiler as a suggestion. The compiler may or may not store the variable in a register.</li>
<li>extern variables are defined in a separate translation unit. These are linked with your code with the linker step of the compilation process.</li>
</ul>';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php