What best practices should be followed when checking for variable existence and value in PHP scripts to avoid errors?

When checking for variable existence and value in PHP scripts, it is important to follow best practices to avoid errors such as notices or warnings. One common approach is to use the isset() function to check if a variable is set and not NULL before accessing its value. Additionally, using strict comparison operators (=== and !==) can help ensure that the variable exists and has the expected value.

// Check if a variable is set and not NULL before accessing its value
if (isset($variable)) {
    // Variable exists and is not NULL, proceed with using its value
    echo $variable;
} else {
    // Variable is not set or is NULL, handle this case accordingly
    echo "Variable is not set or is NULL";
}