11. String and Interpolation Model

KAL string handling is a KAL-layer rule rather than a native KDL string feature.

String literals used in operator bodies are interpreted according to the KAL string model.

The current draft accepts these KAL string literal forms in operator bodies:

• ordinary quoted strings
• multi-line strings
• raw strings
• raw multi-line strings

Only ordinary quoted strings and multi-line strings are interpolation-capable.

Raw strings and raw multi-line strings are treated as literal string values and do not perform ${...} interpolation.

The current draft does not define bare identifiers as KAL string literal forms.

Declaration-time strings in component headers are not interpolated.

The only interpolation form is:

${reference}

Rules:

• reference must be a valid KAL reference
• interpolation does not support expressions
• interpolation does not support function calls
• interpolation does not support nested interpolation
• \${ means a literal ${ sequence inside an interpolation-capable string
• ${ without a matching closing } fails validation
• ${} fails validation
• ${...} whose contents are not a valid KAL reference fails validation

Current interpolation value contract:

• scalar values such as string, number, and boolean are valid interpolation inputs
• object and array values are not implicitly stringified
• if a non-scalar interpolation value is statically knowable, validation should fail
• otherwise, a non-scalar interpolation value fails when interpolation is attempted

Reference fields used by core document-loading or data-loading semantics must not rely on general interpolation in the current draft.

Interpolation is evaluated before the resulting string value is passed to an operator or bound by core.assign.

Multi-line string values follow the same interpolation model as ordinary quoted string values.

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