Conventions follow platform and writing direction; they cannot be copied globally

What it is

iOS Back lives top-left. Android up-navigation also lives top-left, but Android still has a system Back key or an edge gesture, so that top-left control is not the same job as iOS Back. Windows close is top-right of the window; macOS traffic lights are top-left. Arabic and Hebrew UIs flip the start edge to the right, and a former top-left Back has to mirror with it, or the start edge sits empty and the end edge holds two ways out. Conventions are local: a slot is written for a platform community and a writing direction, and cannot be pasted as a global coordinate.

An “international” board of top-right close, top-left back, lower-right primary can point at the wrong slot on every one of those axes.

Why it happens

A convention comes from a shell a community has repeated, not from a universal philosophy of space. Platforms write leave, forward and primary into different slots, and users’ motor programs follow that shell. Writing direction then flips the start/end axis: start is home for back and up-a-level, end is home for forward and more. An unmirrored LTR shell in RTL sends Back to the end edge, crowded with More, and the start edge becomes a blank nobody asks.

Copying across platforms also stacks jobs. Paste iOS’s top-left Back onto Android, which already has system Back, and “leave” exists twice; people cannot tell which closes one layer and which pops the whole stack.

Where it stops holding

Some icon directions must not mirror (play, progress) while positional conventions still must — the two are often wired to one “mirror everything” or “mirror nothing” switch, and have to be split. A game that ships its own chrome across platforms can ignore the host, but then has to keep its set on every platform, not follow the system on iOS and itself on Android. The Web in a desktop browser faces Windows and macOS users at once; the close slot cannot please both. A common repair is to follow the content’s writing direction and compensate with an explicit Close word.

Applying it

• Specify close, back and primary per platform. Do not cover iOS, Android and desktop with one international artboard.
• Turn on positional mirroring for RTL: navigation and primary follow the start/end flip; play, timelines and numerals do not.
• Where Android already has system Back, the app’s top-left is Up, not a second Back of unclear duty.
• How to check: the same flow on iOS, Android and one RTL language — leave this layer / go up a level / primary. A first landing on the other command on any of them means the slot-set was copied from another community.

Related

• Same group: F1.14.1 Positions acquire fixed meanings through long use, such as top-right for close or more · F1.14.2 Putting things off the platform convention raises search cost · F1.14.4 A new convention takes long, consistent exposure before it holds
• Nearby: E1.18 Button order and platform convention · F3.09 Position and hierarchy
• Search terms: convention locality · RTL mirroring · platform convention