Notify URL and Return URL is used in Paypal Payment Gateway integration. Notify URL is used by PayPal to post information about the transaction. Return URL is used by the browser; A url where the user needs to be redirected on completion of the payment process.

The function unlink() is to remove a file, where as unset() is used for destroying a variable that was declared earlier.

Htmlentities() converts all applicable characters to HTML entities. While htmlspecialcharacter()converts special characters to HTML entities. This means htmlentities( ) will check for non English language characters, such as French accents, the German umlaut, etc.

Copy() makes a copy of the file. It returns TRUE on success. It can copy from any source to destination. Move simply Moves the file to destination if the file is valid. While move can move the uploaded file from temp server location to any destination on the server. If filename is a valid upload file, but cannot be moved for some reason, no action will occur.

To pass the information into the script from outside, help can be taken from the PHP CLI (Command line interface) method. Suppose addition of two numbers has to be passed to PHP then it can be passed like this on the command line:

php add.php 2 3

Here the script name is add.php, and 2 and 3 are the numbers that has to be added by the script. These numbers are available inside the script in an array called $argv. This array contains all the information on the command line; the statement is stored as follows:

$argv[0]=add.php

$argv[1]=2

$argv[2]=3

So, $argv always contains at least one element — the script name.

Then, in your script, you can use the following statements:

$sum = $argv[1] + $argv[2];

echo $sum;

$argc is a variable that stores the numbers of elements in $argv. $argc is equal to at least 1, which is saved for the name of the script. Example is $argc=3 using the above statements.

The difference lies with the execution of the languages. PHP is server side scripting language, which means that it can’t interact directly with the user. Whereas, JavaScript is client side scripting language, that is used to interact directly with the user.

Notices, Warnings and Fatal errors are the types of errors in PHP

Notices: 

Notices represents non-critical errors, i.e. accessing a variable that has not yet been defined. By default, such errors are not displayed to the user at all but whenever required, you can change this default behavior.

Warnings: 

Warnings are more serious errors but they do not result in script termination. i.e calling include() a file which does not exist. By default, these errors are displayed to the user.

Fatal errors: 

Fatal errors are critical errors i.e. calling a non-existent function or class. These errors cause the immediate termination of the script.

- Positioning: Is some what where we need the object to be placed in the graphical view i:e on screen. If we talk in DHTML sense then we have two types of positioning: Relative and Absolute.

Relative Positioning: Relative positioning is the same as the current HTML3 layout and is best reserved for situations where you want to be sure that the content will revert to this default inside a document that also uses absolute positioning.

Absolute Positioning: In DHTML absolute positioning means that the object will remain at the same position regardless of the condition of other elements and the size of the browser. In simple languages if an object/image is absolutely positioned (STYLE="position: absolute;"), with an offset of 150 pixels to the right and 250 pixels down from the left-hand corner of the browser screen then it will avail this position what ever the circumstances may be.

- Style Modifications: Style modification indicates the changes in the presentation or the view part that are being made in web page. This part comes under Cascading Style Sheet where the user style his web page by using the attributes and the tags that are pre-defined in CSS.

- Event Handling: As explained earlier Events is the beating heart of any JavaScript application. For handling event in DHTML we attach event handler to HTML elements. The event handler waits until a certain event, for instance a click on a link, takes place. When it happens it handles the event by executing some JavaScript code that has been defined by us. After it has executed the code the event handler comes to its initial state and waits for the user to fire any event. Hence to handle events in DHTML we need to register an event handler.