Web structure, presentation, scripting and publishing
Web development connects content structure, visual presentation and behavior. HTML describes the document and its semantics, CSS controls presentation, and JavaScript can respond to events and manipulate a document through defined browser interfaces. These roles overlap in a rendered application but should not be confused.
Use meaningful elements and labels rather than choosing tags only for their default appearance. A heading identifies a section, a button represents an action, and a link navigates to a resource. Form controls need understandable labels and useful feedback. Keyboard operation, visible focus, sufficient contrast and text alternatives help make a page usable for more people; an attractive screenshot alone does not establish accessibility.
CSS applies rules through selectors and a cascade. Specificity, source order, inheritance and property behavior affect the final style. A layout can change with viewport size without changing the underlying content meaning. Test actual reading order and interaction rather than assuming that visually moving a component also changes how assistive technology encounters it.
JavaScript works with values, control flow, functions and events. A handler should distinguish the event target and the intended action, and code should account for missing or unexpected input. Client-side validation can improve feedback, but it does not replace validation and authorization on the trusted server. A user can alter requests or bypass the browser interface. Output handling must match the actual context rather than inserting untrusted text as executable markup.
A content-management system separates stored content and publishing workflows from some presentation work. Roles and permissions still matter, and a plug-in or template does not guarantee security or correct licensing. Previewing, reviewing, publishing and maintaining versions are different steps. A public link can expose information even when the author did not intend broad distribution.
For digital images, distinguish dimensions, resolution, color representation and file compression. In a supplied uncompressed model, a 4 by 3 pixel RGB image with 8 bits per channel uses 4 times 3 times 24 bits, or 36 bytes, before headers or other overhead. A compressed file need not have that size. Choose a format for the required transparency, detail, scalability and editing workflow rather than assuming one extension is always smallest or best. These are common foundations, not a promise that every browser or software version exposes identical controls.