Visual designation of a zone in rendered code

A non-transitory computer readable storage medium having computer-readable code stored thereon, which, when executed by at least one hardware processor, causes said at least one hardware processor to:

• execute a client-side script by a web browser upon the web page being displayed in the web browser, to:
• (a) analyze a tag structure in a source code of the web page, to establish a Document Object Model (DOM) of the web page;
• (b) create a Graphical User Interface (GUI) for visually designating the placeholder;
• (c) detect a user selection, made using the GUI, of a location in a graphical view of the web page;
• (d) update the DOM of the web page on the fly, to render the web page and display the placeholder in accordance with the user selection;
• (e) compose instructions for injecting a content element in the location of the user selection;
• and
• (f) transmit the instructions to a remote server.