A keystroke builds an editable structural model; the same packaged mathtex (XeTeX) engine that powers the renderer typesets it to SVG in WebAssembly; and the caret / selection are placed by matching the model back to the IR's source spans. There is no LaTeX parser — you type math and the editor builds the tree. No server.
Click to focus, then type. sum/int/alpha+space → symbols ·
/ fraction · ^/_ scripts · ( [ delimiters ·
sqrt+space radical · <=→≤ · +-→± · arrows navigate
(right exits a slot) · Backspace deletes structurally · Tab jumps between empty slots.