What gets magnified in a focus-plus-context view has to be the user's choice, not the system's

What it is

In focus plus context, the decision "what gets magnified" must rest with the user: hover-follow, a draggable focus frame, click-to-focus are all fine — but the system alone may not choose. A fixed focus demotes the pattern to a static close-up: the context survives, the explorability dies, and explorability is exactly what the pattern was brought in to buy.

Why it happens

Movability is what separates focus plus context from a zoomed screenshot: exploration is user-driven interest transfer — attention moves, and the focus should follow; a fixed focus means the system has pre-judged the user's interest path, and the definition of exploration is precisely that the path cannot be pre-judged. The choice of movement mechanism shapes the cost of use: hover-following is cheapest but misfires easily (everything swept past gets magnified), while click/drag is precise but adds a step. The two commonly coexist: hover to preview, click to lock. The movement response must also be real-time — the warp should track the dragging focus continuously; laggy deformation destroys the user's sense of control over the mapping.

Where it stops holding

Movable does not mean unconstrained: the focus movement's boundaries (edge-of-canvas handling), its granularity (per element or per pixel), and its conflicts with scroll/pan gestures (does dragging move the focus or the view?) all need explicit conventions, or movement itself becomes the mis-operation source. Touchscreens have no hover, so focus movement rides taps and drags at higher cost — the pattern's suitability must be reassessed there. In collaborative or presentation settings, auto-following the presenter's pointer is a legitimate controlled-automatic mode, but final control must still return to the user.

Applying it

• Offer at least one movement mechanism: hover-following (preview) plus click-to-lock (confirm) is the universal pair.
• Make focus dragging respond in real time and keep it clearly separated from panning (say, hold a modifier to move the focus).
• Verification: have users move the focus to a target position and dwell to read; smooth movement with no misfires passes — frequent mis-placement means gesture conflict; re-allocate the interactions.

Related

• Same group: U6.06.1 Focus plus context keeps detail and global in one view · U6.06.2 The difference from overview-plus-detail is whether they occupy two views · U6.06.3 The transition between focus and context must be continuous and legible · U6.06.4 The pattern saves gaze switches but adds spatial comprehension load
• Nearby: U6.07.3 Distortion shifts as the focus moves; targets drift and become hard to hit · U6.09.2 Touchscreens have no hover and need alternative paths
• Search terms: movable focus · degree of interest function · interactive lens