Any cross-domain request is under security control. Its goal is to protect the server with old standards from hacking attack. “Old” mean those servers that do not even suspect that pages can send queries with the methods “PUT”, “DELETE”, etc.
For a clear classification, the CORS specification divides all requests into two types: simple requests and incomplete requests.
An HTML document is a text file marked with special (textual) commands. The text format for submitting web documents was selected based on the basic requirements for a web document: simplicity, the ability of direct interpretation in any operating system, the minimum file size, ease of editing and interpretation.
All sites are divided into static and dynamic ones according to their structure and capabilities. If you create static site all content of its online resource will be stored at the site and If you create a dynamic site, then all the information will be stored separately from the basic information on the site.
When design is created, when all functionality modules and components should be connected together page layout is final stage of site development, site structure that will define the text and graphics on the site in different browsers. There are fixed and changeable layouts of the site. When layout is fixed all elements of web-pages always have a fixed size, regardless of monitor size set by the user and screen resolution.
Usability means convenience and simplicity in using of site. So you have a few minutes to say a lot to user and explain accessible what he needs to do and where necessary information is. You should take into consideration that users don’t read texts on sites like newspapers they look through it very quickly. «More easily-more better» it is typical principle for usability.
To open such site user needs to load its page and all changes on page which don’t need any new data are implementing faster because they don’t wait for inquiry processing on server. Such conception of web-site derived it’s name SPA(Single Page Application). Single Page Application try to take the best from web-site and native application.