HTML you can paste somewhere.
The pane on the right is the conversion, as text. It is produced by the same engine that draws the paper on the left — html_document in mori's core, the function the desktop app calls when you export. Edit on the left and the HTML follows on the next keystroke.
All four combinations come from the engine: a full document with the stylesheet the desktop app exports, the same document without it, and the body markup on its own. Nothing on this page carves up the engine's output with string surgery.
Relative images
An image written as  converts to a relative src, unchanged. That is correct and it is also the single most common way a paste comes out broken: the path only resolves if the HTML ends up next to the same folder of files. Before pasting anywhere that is not your own static site, make image paths absolute URLs in the Markdown first. The conversion will carry them through untouched.
Code highlighting
Fenced code keeps its language on the element, and the colouring rides along in the document's style block. Take the styles away and the code is still code — structure, spacing and monospacing intact — just monochrome. Highlighting that survives a strip has to be per-token inline styles, which is a much heavier document; mori does not emit that.
Inline styles, or a style block
A full document carries one <style> block in the head and clean, class-free markup below it. That is the right shape for a file you open in a browser or host as a page, and the wrong shape for two places: email clients, many of which drop the head entirely, and CMS editors that strip style blocks on save. For those, the body-only output plus the destination's own styles is the combination that holds.
What breaks, and where
Nothing leaves the tab
The engine is compiled to WebAssembly and runs in this page. Your Markdown is not uploaded, and there is no account. Close the tab and the document stays in this browser only.