Clipboard

Implementation notes and historical checks. Open the visual guide →.

On Windows and macOS, select drawing objects and use Ctrl+C / Cmd+C to copy editable structure data together with image alternatives. Ctrl+X / Cmd+X cuts only after the clipboard write succeeds. Ctrl+V / Cmd+V inserts supported drawing data as one undoable edit. The private ReShiki representation retains the full supported document model, including groups and custom presentation fields.

Use Ctrl+Shift+C / Cmd+Shift+C, or Export → Copy image, for a picture of the selection. With nothing selected, it copies the whole drawing. This supplies PDF, 1200 dpi PNG and SVG; a raster-only drawing representation also carries explicit publication-size bounds for compatible drawing applications. A pasted picture does not contain editable atoms or bonds. View aids such as grid, rulers and crosshair are excluded.

On Windows, normal Copy supplies an editable Office object with the full drawing and a cached preview. Double-click opens ReShiki; Ctrl+S updates the open Office document. Copy Image supplies a static figure with SVG text converted to outlines to preserve label placement. SVG file export continues to contain text. Office editing steps.

Office and macOS

Windows desktop Office supports ReShiki OLE objects. Copy the object back into ReShiki to recover its native drawing; Paste picture explicitly reads its preview. Copy Image remains the command for applications that only accept pictures. Normal Copy omits standalone PNG/SVG/bitmap formats because Word prefers them over the editable object; it retains the metafile presentation required by Office.

Clipboard PNG figures have a transparent background on Windows and macOS. The Windows editable object’s EMF+ dual preview keeps bonds and outlined text as vectors, preserving smooth edges when enlarged. It also preserves transparency, including partially transparent imported pictures. The standard Windows bitmap fallback and PNG file export have a white background. Open an older embedded ReShiki object and press Ctrl+S to refresh its preview, then save the Office document.

macOS retains its existing native drawing/CDX and PDF/PNG/SVG clipboard representations. Mac Office does not provide this Windows OLE activation workflow; even ChemDraw documents have different editing mechanisms on the two platforms (Revvity’s interoperability guidance). For reliable editing across Windows and Mac, keep the .reshiki original, edit it in ReShiki and replace the Office figure. A pasted picture alone cannot restore native atoms and bonds. Mac Office round-trip behavior has not been verified by this Windows test run.

Editable external exchange uses the supported binary CDX/CDXML subset. It covers tested molecules, formal charges, isotopes, tetrahedral and double-bond stereo, bond/label colors, styled text, supported arrows, graphics, embedded raster pictures and nested groups. Some scientific symbols and orbitals become editable vector paths rather than retaining their original preset type. If the receiving editor asks which document settings to use, preserving the copied settings retains the source appearance.

Paste prefers native drawing data and explicit external chemical formats, then PNG/JPEG/TIFF/WebP pictures, then plain chemical text. Unsupported editable content produces an error rather than silently substituting a picture. Ctrl+Shift+V / Cmd+Shift+V or Import → Paste picture explicitly chooses a raster representation, including when editable formats are also present.

Boundaries

• Picture paste creates one embedded object and one Undo step. Native ReShiki Copy/Paste preserves a picture’s frame, orientation and transparency. Copy Image also supplies a native raster object so normal Paste retains its publication size; PNG paste honors resolution metadata. Picture controls and limits.
• External editable exchange retains pictures as separate objects alongside chemistry, with physical bounds, rotation, transparency and groups. Reflections are stored in the picture pixels without resampling. Embedded vector/OLE-only pictures remain unsupported. Formats and limits.
• Binary exchange shares the documented CDXML restrictions. Query/reaction predicates, unsupported objects, polymer semantics and enhanced stereo are not supported. External text metrics can differ. Binary paragraph line spacing is rounded to whole points; native documents and image exports retain their own precision.
• If external editable export is unavailable, Copy still provides the native ReShiki drawing and available images, with a visible notice. Image representations that fail to render are also reported.
• The binary codec accepts up to 16 MB. Native integration limits all representations to 64 MB combined and the rendered raster to 80 million pixels. Large drawings can exceed the combined clipboard limit before reaching the raster limit; file export remains available.
• Linux uses the earlier text clipboard path; picture file import is available in the app. Windows Copy Image supplies CF_DIB alongside PNG, PDF and SVG. Only ReShiki’s own OLE objects are read as editable native documents; arbitrary embedded objects are not activated or imported. See the Windows guide.
• CDX is currently exposed through the clipboard and internal worker; the file Open/Export UI does not yet offer it.

Verification

Native desktop tests copied a 13-atom, 13-bond aspirin drawing with red bonds and teal labels into another drawing editor, then copied it back into ReShiki. The returned binary data retained the molecular identity, counts and colors. A separate image paste retained the publication dimensions instead of expanding to the PNG’s pixel dimensions. The standalone worker was launched outside the checkout.

Automated tests cover independent native clipboard data, supported exchange fixtures, Unicode font runs, large property lengths, truncation, duplicate identifiers, invalid base64, query rejection, stale asynchronous completion and failed Cut. The raster wrapper is checked for image-only contents, unchanged PNG bytes and physical bounds. Local desktop artifacts are under artifacts/clipboard-qa-20260920/ and are ignored by Git. These examples establish the tested subset, not universal external-document compatibility.