Interaction & control — router

This plugin holds the principles that govern interaction: what is clickable, what happens when it's clicked, how mistakes are prevented and recovered. They apply to web, mobile, desktop, voice, and physical product interfaces.

Principles in this plugin

Each principle has its own skill (with sub-aspect skills where useful). Principles marked [full] have reference-grade skill files; the rest are planned and will be added in subsequent passes.

Affordance and target sizing

• affordance [full] — visual and behavioral cues that suggest how an element is used.
  • Sub-skills: affordance-buttons-vs-links, affordance-disabled-states, affordance-non-obvious-targets.
• constraint — limit interactions to those that are valid in context.
• fitts-law [full] — time to acquire a target depends on its size and distance.
  • Sub-skills: fitts-law-touch-targets, fitts-law-screen-edges, fitts-law-pointer-acceleration.
• defensible-space — separate destructive controls from common ones.
• entry-point — the first point of contact must invite engagement.

Feedback and errors

• feedback-loop — every action gets a perceptible response.
• errors — slips (skill failures) vs. mistakes (knowledge failures); design for both.
• forgiveness — make actions reversible or confirmable.
• garbage-in-garbage-out — validate at the boundary; don't let bad data flow inward.
• cost-benefit — don't ask the user to pay for an action whose payoff isn't clear.
• convergence — design conventions converge over time; deviate only with reason.

Control and behavior

• control — users should feel in command of the system, not the reverse.
• flexibility-usability-tradeoff — every added option harms usability for the simple case.
• most-advanced-yet-acceptable — push novel only as far as users will tolerate.
• performance-vs-preference — what users prefer isn't always what makes them effective.
• hierarchy-of-needs — functionality, reliability, usability, proficiency, creativity (in order).

Persuasion and behavior shaping

• nudge — small choice-architecture changes that make the better path easier.
• operant-conditioning — behavior shaped by reinforcement; use sparingly and honestly.
• classical-conditioning — emotional associations transfer.
• shaping — gradually increase task complexity through practice.
• expectation-effect — users perceive what they expect to perceive.
• freeze-flight-fight-forfeit — under stress, users default to instinctive responses.
• desire-line — the path users actually take, often diverging from the planned one.
• interference-effects — competing stimuli (Stroop) slow processing.

Heuristic for which to read first

• Designing buttons/CTAs → affordance, fitts-law, defensible-space.
• Designing forms → affordance, constraint, feedback-loop, errors, forgiveness.
• Mobile target sizing → fitts-law-touch-targets.
• Destructive actions → defensible-space, forgiveness, freeze-flight-fight-forfeit, expectation-effect.
• Validation and error copy → errors, forgiveness, garbage-in-garbage-out.
• Modal vs. non-modal decisions → control, entry-point, interference-effects.
• "Should we add this option?" → flexibility-usability-tradeoff, most-advanced-yet-acceptable.

Cross-plugin pointers

• For visual layout, hierarchy, and grouping, see perception-and-hierarchy-principles.
• For learnability (mental models, defaults, recognition), see cognition-and-learnability-principles.
• For aesthetic and tonal decisions, see aesthetics-and-emotion-principles.
• For accessibility, see process-and-robustness-principles.