Is there a way to set a page level variable which can be used across components (By Content Authors or System Developers) in the page?
e.g. I have a query string parameter in the page URL (www.mysite.com/start.html?product=chair). I want to set the value 'chair' in some page level variable so that when content authors write the content they can use this variable in any component on the page using something like PAGE_VARIABLE[product]. Same variable can be used in system developers in their code as well.
Have you tried using design components? Site level values can be stored there, and editors / authors can update those values via the Design context. You can specify a template's designPath as the Global path (eg. home page template), and any design level updates to that design path can be used across any template by accessing the value via code.