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Canvas SDK
Text and expressions

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Text and expressions

What an attribute’s text becomes: rich text and its footnotes, live values, symbol names, measured and wrapped labels, and a compiled expression.

@internote/canvas-sdk51 exports

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Functions Classes Constants Interfaces Types

An author's text is rarely plain: a label can hold bold, links, maths, symbols and live values. This area covers what that text becomes, and the maths behind expressions.

Rich text. renderRichText draws inline content as React nodes. flatten turns it back into a plain string, for alt text or measuring.

Live values. When an author writes {{#f.slope}}, prose shows a number the canvas computed. LiveValueStore holds those numbers: an environment publishes to it, and the text reads from it.

Measuring labels. textWidth, wrapWidths and balancedWrap measure and wrap a label before it is drawn, so it can be placed where it fits.

Expressions. evaluateExpression evaluates an author's maths safely, with parameter values injected. compileSafeExpression compiles one to a function once, for code that samples it thousands of times. compileComplexExpression and evaluateComplexExpression do the same for complex numbers.

#Functions

Returns the box a label needs when the browser balances its lines rather than filling them greedily.

chalkExpressionOf

The bound expression an attribute value carries, or null for an ordinary one.

The installed runtime, or null where none is yet.

chalkRuntimeSettled

Whether asking for the runtime has come to an end: it is installed, it failed to load, or there is nothing that could load it.

The variables the document's controls introduce (D68) — every slider's and selector's letter — while a document is being refined, so a value the compiler never saw (a frame of a keyframe chain, a reader's edit) is typed with the same letters bound that the document's own positions had.

compileComplexExpression

Compiles a complex expression once, with its parameters fixed, into a function of its variables, or returns null when the expression is refused.

compileSafeExpression

Compiles an expression's JavaScript to a function of the given formals, or returns null where the formals or the body fail the checks or JavaScript refuses the result.

evaluateChalkExpressionNode

Evaluate a tree.

evaluateChalkPayload

Evaluate a whole payload to whatever the compiler gives: a number, a boolean, text, a list (a mark's colours, one per item), a record, null for an application that chose no value, or { apply } for one the host finishes (D69).

evaluateComplexExpression

Evaluates a compiled complex expression once, or returns null where it fails to evaluate or comes out non-finite.

evaluateExpression

Evaluates a compiled expression with the given parameter values, or returns NaN when it cannot.

expressionItemOf

Returns the bound expression an inline content item carries, or null for a text run or a micronode.

Converts inline content to a plain string with its formatting dropped, as a maths run's text is handed to KaTeX.

formatLiveValue

Formats a live value for display in text: about four significant figures, or an em dash when there is no value yet.

Returns whether a label value has anything to draw: a non-blank string, or inline content with a text run, a bound expression or a micronode in it.

installChalkRuntime

Installs the compiler's exports.

Returns whether a value is a Complex: an object with numeric re and im.

isSafeCompiledExpression

Returns whether a value is an expression the compilers could have emitted over these formals, and so may be compiled.

isSafeFormalName

Returns whether a name may be a formal of a compiled expression: an ASCII identifier, and not a reserved word.

Returns whether a value is the name of a symbol the language has a drawing for.

Converts an element's text-size: to pixels at the environment's scale factor.

Wraps a LaTeX string as inline content, a label that is one maths run.

needsChalkRuntime

Whether a compiled value holds anything only the runtime can decide, at any depth: a condition, an application, a #self reading — any tree the compiler did not already finish.

Returns what a label will look like once set, near enough to count its characters and measure it.

requestChalkRuntime

Starts loading the runtime, if a loader is set and nothing is installed.

Returns a document-supplied link target as it may be rendered, or undefined when it may not be.

setChalkRuntimeLoader

Sets how a page gets the runtime when nothing has installed one — the browser build fetched and instantiated.

subscribeChalkRuntime

Calls listener whenever the runtime arrives or fails to.

Returns how wide a piece of text is at a size in a face, in pixels, measured by the browser where there is one and estimated from an average glyph where there is not.

withDocumentVariables

Runs fn with chalkVariables answering names, and restores what it answered before.

Returns the width of each line a greedy word wrap at a width produces, measured in the face the text will be set in.

#Classes

The document's live values, keyed by node id and member: what a derived attribute publishes and a {{#id.member}} reads.

#Constants

The CSS font stack labels are set in: the reading serif, falling back to Georgia.

The text-size: value that gives a label the standard size, LABEL_SIZE.

The default label size in pixels, before the environment's scale factor is applied.

MATH_NAMESPACES

The namespaces a real expression reaches: Math alone.

What each symbol is called, in words: the alt text for a drawing, and the fallback reading for speech.

#Interfaces

The two compiler exports the SDK calls after a document has compiled.

A complex number, which is also the compiled value of a complex literal.

A compiled inline item as the text helpers read it: a text run, a bound expression, or a micronode.

LiveValueFormatOptions

Options for formatLiveValue.

RichTextCitationArgs

What RichTextOptions' renderCitation receives for one citation marker.

RichTextFootnoteArgs

What RichTextOptions' renderFootnote receives for one footnote.

One item of inline content: a text run, a bound expression, or a micronode such as bold or link.

RichTextOptions

How renderRichText renders: where the text is shown, and the host's own renderers for the nodes that need the host's data.

#Types

ChalkExpressionNode

One node of a compiled expression tree.

ExpressionNamespaces

A namespace an expression may reach members of, by name: Math, or a runtime such as the complex cx.

A list a construct publishes, one entry per item: a number each, as a fit's residuals, or a point each, as its readings and fitted.

A value the store holds for one #id.member: a number, which is nearly everything; the text or truth value a question publishes as its verdict, its response, correct and answered; or a list, item by item.

One live value to publish, as [nodeId, member, value].

RichTextContext

Where rich text is shown, which picks the context variant of some classes (bold, code, links, footnotes).

Last updated 26 September 2026

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