Clipboard

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

Cmd/Ctrl+C copies the drawing for ReShiki, ChemDraw, Office and image apps. It offers editable drawing data and image alternatives, with no chemical plain text. This behavior is the same on Windows, macOS and supported Linux desktop sessions. Cmd/Ctrl+X cuts only after the clipboard write succeeds. Cmd/Ctrl+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, PNG and SVG; PNG starts at 1200 dpi. On Windows, large raster previews use a lower resolution to fit clipboard and picture limits, with a notice showing the actual DPI. Resolution metadata preserves the physical size; editable drawing data and vector formats keep their precision. 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.

Pictures use the canvas colors with a transparent background. Switch the canvas to black for dark slides, and to white for light slides.

What Paste uses

Cmd/Ctrl+V tries the available formats in this order:

ReShiki drawing data.
ChemDraw CDX, then CDXML.
MOL, then SMILES offered as chemical formats.
Plain text that imports as chemistry: MOL, SMILES, reaction SMILES, InChI, RXN, CDXML or ReShiki clipboard JSON.
PNG, TIFF, JPEG, then WebP pictures.
Other plain text, PDF or SVG use the usual error messages if nothing can be pasted.

On Windows, drawings embedded in Office objects are tried first. If a format fails, Paste tries the next one. PDF and SVG pictures need conversion to PNG. If every available format fails, Paste explains the problem. For a drawing from a newer version, the message asks you to update ReShiki. Import → Paste picture prefers pictures even when editable formats are present.

Copy chemical text

To paste a structure into a text field such as SciFinder’s, select it and use Cmd/Ctrl+Alt+C. With no selected reaction arrow, this copies molecular SMILES. With one clear reaction arrow and complete participants, it copies bounded ChemDoodle reaction JSON. Explicit reaction roles take precedence; an unassigned forward arrow can supply roles from the molecules’ positions for this copy only. Ambiguous or unsupported chemistry leaves the previous clipboard intact and reports the reason. See reaction selection rules and the SciFinder handoff.

Cmd/Ctrl+Alt+O copies MOL text. Both text shortcuts require a selection. Select the complete molecule to avoid exporting only a fragment.

The command palette’s Copy SMILES, Copy CDXML and Copy MOL rows copy the selection, or the whole drawing when nothing is selected. Their keyboard shortcuts still require a selection.

Copy as

Right-click and choose Copy as… to choose one format: PNG, SVG, PDF, MOL, SMILES, InChI, Name, CDXML, CDX, RXN · V3000, Reaction SMILES, or ChemDoodle JSON · reaction. The submenu says selected objects when there is a selection and whole drawing otherwise. It uses the same selection rules as ordinary Copy, retaining required abbreviation and attachment members. It does not automatically select the rest of a partially selected molecule; use Select molecule first when that is what you need.

Name requires one complete connected molecule and generates its name locally, accepting it only when parsing the name reconstructs the same structure. It copies unchanged plain text alongside HTML with italic descriptors and superscript element locants, and RTF in the desktop app. Copy name in the Chemical names inspector uses the same rich text formats. Text fields can use the plain name, while rich text editors can retain its typography.

PNG, SVG and PDF copy the visible figure without the canvas background. Molecular formats copy chemical data, not captions or figure layout. Select a molecule within a reaction for MOL, SMILES or InChI. RXN and reaction SMILES require one complete, explicitly defined reaction with reactants and products; a drawn arrow alone does not assign roles. The submenu explains unavailable formats. CDXML and CDX use the strict drawing exporters and do not silently substitute a picture when a feature cannot be represented.

A text-label refusal names the first label and counts any others. It suggests ordinary Cmd/Ctrl+C as an editable-copy alternative and native .rsk to keep the complete drawing. Ordinary Copy can still use its documented picture fallback when editable exchange is unavailable. Inner ring curves have their own refusal. Long status messages show a visible … beside the text; hover over the message or that cue to read the full explanation.

Conversion finishes before the clipboard changes. If conversion fails, or the drawing or selection changes before it is ready, the previous clipboard stays intact. Format warnings appear in the copy receipt. Switching tabs keeps the request with its source drawing; closing that tab before preparation completes discards it. No drawing, selection or Undo history is changed by Copy as.

ChemDoodle JSON · reaction prepares plain text for a compatible sketcher’s explicit JSON import, using the published ChemDoodle JSON schema. It preserves reactant/product membership through the arrow’s atom-ID references, molecular connectivity, coordinates, charge, isotopes and attached hydrogen counts. Separate explicit H atoms remain separate. It currently requires one forward reaction, one connected molecule per participant and coefficients of one. Valid aromatic molecules use Kekulé single/double bonds with preserved attached hydrogen counts. Agents, atom maps, stereo (including stereo inferred from geometry), radicals, special bonds, attachment atoms and collapsed abbreviations are rejected before the clipboard changes. Captions and drawing styles are omitted with a visible receipt notice. The copied text does not contact CAS or submit a search; see the manual SciFinder handoff.

Text formats also provide ordinary clipboard text. On platforms without native clipboard support, SVG text copies the SVG markup; PNG, PDF and CDX remain unavailable and can be exported as files instead. Copy as remains an explicit choice of format. The chemical-text, MOL and CDXML shortcuts use the same conversion and warning handling, and require a selection.

Tracked in #110. Clipboard recipients choose which offered representation they accept; a successful copy does not establish that another application imported it correctly.

Office and macOS

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.

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.

Normal Paste also reads supported ChemDraw CDX stored inside a Windows Office object. In PowerPoint, select the whole embedded object on the slide, copy it, then paste into ReShiki to recover editable atoms and bonds. Embedded drawings are tried before the other clipboard formats. If embedded data cannot be read, Paste tries the remaining formats, including pictures. Import → Paste picture chooses the preview. Validation and review checklist.

Clipboard PNG, PDF and SVG figures always have transparent backgrounds. They retain the visible ink: black bonds and labels from a light canvas, white bonds and labels from a dark canvas. The Windows editable object’s EMF+ dual preview keeps bonds and outlined text as vectors. Imported pictures retain their own pixels and transparency. Open an older embedded ReShiki object and press Ctrl+S to refresh its preview, then save the Office document.

Dark editable ChemDraw copies use white bonds and labels without a background rectangle. Pasting between ReShiki drawings adds no page background; Ink and palette colors follow the receiving drawing’s canvas and theme, and custom colors stay exact. View → Interface affects only the app controls; it never changes clipboard output.

macOS retains its existing native drawing/CDX and PDF/PNG/SVG clipboard representations. Mac Office does not provide this Windows OLE activation workflow. Keep the .rsk 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.

MOL text copied from a chat or web page imports even when the copy drops leading spaces from its lines. A structurally valid drawing can be pasted even if chemical validation fails; its atoms, bonds and supplied charges are preserved, with a review notice and no molecular properties.

Editable ligand copying

Use ordinary Cmd/Ctrl+C and Cmd/Ctrl+V in both directions. Cp and arene examples retain editable ring atoms, aromatic bond orders, perspective edges and multicenter attachment targets. Cp’s hidden −1 charge is carried by an invisible attached charge symbol; it is not removed from the chemical data. Metal charges remain as entered. Returning these drawings to ReShiki reconstructs one aromatic ellipse per ring, without extra C/H labels or a duplicate curve.

The shortcut gallery is supplied as editable CDX on the clipboard even when its high-resolution PNG would be too large. Keep the .rsk original for complete projection depth and ReShiki-specific editing metadata.

When a receiving editor returns R/X as query nicknames, ReShiki imports them as uninterpreted atom text with a notice. Molecular properties and query semantics are unavailable for that drawing; other unsupported query types remain rejected. NO2/N3 group definitions retain their formal charges through the tested return copy. Before/after captures and return-paste verification.

Styled metal contacts are also retained when chemical normalization would otherwise turn their single bonds into coordinate bonds with incompatible wedge styles. That import keeps the supplied drawing, reports that coordination assignments need review, and withholds molecular properties.

Changes made for an external copy

Feature	Editable CDX clipboard behavior
Cp/arene perspective, aromatic ellipse and attachment targets	Preserved in the tested desktop round trip.
Hidden ±1 charge on an aromatic carbon without other marks	Retained as an invisible attached symbol.
Other hidden charge labels	Shown in the external copy; charge values are retained.
R/X and other variable text	Kept as an uninterpreted atom label; variable/query semantics are omitted.
ChemDraw 26 groups with numbered attachment points, such as SiMe₃	Pasted or opened as editable structures; each numbered attachment point becomes an ordinary bond.
Partial inner-ring curves	Omitted; the underlying bond orders remain.
Perspective emphasis outside supported aromatic/Haworth cases	Copied as plain bonds when no assigned stereocenter is affected.
Compact groups with multicenter attachment points	May expand into their editable constituent atoms in the receiving editor.
Retained 3D tilt coordinates and ReShiki-specific presentation metadata	Preserved by native `.rsk` and the private clipboard representation; not guaranteed through external CDX.

Copy reports any applied simplifications. File export stays strict. Unsupported content beyond these conversions uses the explicitly reported picture fallback. These limits do not change the source drawing.

Ring interiors copy as ChemDraw native ColoredMolecularArea objects linked to their ring bonds. The fill stays attached when atoms move, and imported fills retain their visible RGB colors. Clipboard images still have transparent space outside the drawing. Older ReShiki-owned filled curves remain readable when their ownership metadata survives.

In the browser

The browser editor uses the page’s clipboard, which holds only text, HTML, PNG and, in Chrome and Edge, SVG. Cmd/Ctrl+C puts a PNG picture of the selection on it, the same picture as HTML for Word, Google Docs and mail, and SMILES as text when the selection has molecules; the picture in the HTML also carries the ReShiki drawing, so pasting it back into a browser editor keeps it editable. Cmd/Ctrl+Shift+C copies just the picture, Copy as → PNG the PNG and Copy as → SVG the SVG with its source as text. Cmd/Ctrl+V tries a ReShiki drawing, then text that imports as chemistry (SMILES, MOL, CDXML, InChI and the others above), then a PNG as a picture; Import → Paste picture takes the picture. Browsers cannot put PDF or CDX on the clipboard, or read ChemDraw’s or Office’s own formats, so use Export for PDF and CDX, and copy CDXML text from ChemDraw (Edit → Copy As → CDXML Text) for an editable structure. The status bar says when a copy or paste worked, or why the browser refused: for example, when clipboard access is blocked for the site or the page is not on https. A page that embeds the editor in its own iframe must allow clipboard-read and clipboard-write.

Text fields, such as the font box, Help search, the Import boxes, captions and property fields, copy, cut and paste plain text through the system clipboard with Cmd/Ctrl+C, X and V, as on the desktop. Pasting into a field uses the browser’s own paste, so it needs no clipboard-read permission or asynchronous clipboard prompt. The clipboard text goes directly to the focused field, including Japanese and other composed text.

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, available images and a sized raster CDX picture, with a visible notice. Other drawing editors receive the picture; ReShiki recovers the editable original. 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. Windows raster previews are bounded to 16 million pixels and 8192 pixels per side, so decoded Office previews and Copy Image bitmaps fit the 64 MB limit; regular editable Copy does not allocate a standalone bitmap that Office would discard. macOS retains its 1200 dpi clipboard raster limit of 80 million pixels. Drawings with large embedded pictures or other encoded representations can still exceed the combined clipboard limit; file export remains available.
Linux supports native drawings, explicit chemical formats, images and text through X11 or the focused Wayland window’s standard clipboard connection. Keep ReShiki focused until Copy finishes; loss of focus or an unconfirmed write leaves a Cut’s source intact. Wayland clipboard data remains available while ReShiki owns the selection; persistence after exit depends on the desktop clipboard manager. X11 uses a persistent owner process until another copy replaces it. Windows Copy Image supplies CF_DIB alongside PNG, PDF and SVG. ReShiki’s own OLE objects are read as native documents; supported ChemDraw CDX can also be read from a foreign object’s bounded root CONTENTS stream. Foreign objects are not activated, and other embedded formats remain unsupported. See the Windows guide.
CDX is exposed through the clipboard and internal Rust chemistry interface; the file Open/Export UI does not yet offer it.

Internal condensed labels such as CCl₂, CF₂ and NMe retain formula typography. When the receiving editor returns an explicit chemical group definition with ordered connections on one attachment atom, ReShiki preserves that definition and both outside bonds. Plain named dummy labels remain uninterpreted text; formatting alone does not assign chemistry.

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.

A seven-atom, six-bond aromatic drawing that fails chemical validation was also copied into ReShiki, back into the source editor, and returned through the native clipboard as editable objects. Both binary captures are regression fixtures. Variable labels now copy as editable uninterpreted atom text; query semantics are not assigned.

A ChemDraw 26 test copied a caffeine drawing with two filled rings into ChemDraw, moved a ring atom, and copied it back. Both fills remained bond-linked native areas with the same visible colors, with no loose curves or pictures. The ChemDraw-created ring and return clipboard captures are regression fixtures in tests/fixtures/ring-fills/.

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.

The macOS adapter maps the portable chemical/x-cdxml representation to ChemDraw’s com.revvity.cdxml, com.perkinelmer.cdxml and com.cambridgesoft.cdxml types, retaining the exact UTF-8 text fallback. NSPasteboardItem requires a UTI, so a MIME string containing / cannot be passed directly. These aliases are declared by ChemDraw 26’s bundle metadata. Unique-pasteboard regressions check the exact native types and bytes for picture and chemical format packets, including ChemDoodle reaction text, and unchanged prior contents after invalid, conflicting or oversized writes. The available Copy as options are listed above. The 64 MB combined limit includes the expanded native aliases.

Linux transport tests additionally cover multi-format selection publication, a 2 MiB X11 incremental image transfer, replacement and one-shot owners, rejected oversized transfer headers, stalled recipients, and atomic rejection of invalid writes. These are isolated Xvfb and process/pipe checks; they do not establish native GUI or compositor-specific Wayland compatibility. Transport design and test commands.