diff --git a/packages/mermaid/src/rendering-util/types.d.ts b/packages/mermaid/src/rendering-util/types.d.ts
index aec99e636..6dabb476d 100644
--- a/packages/mermaid/src/rendering-util/types.d.ts
+++ b/packages/mermaid/src/rendering-util/types.d.ts
@@ -4,4 +4,5 @@ export interface MarkdownWord {
   type: MarkdownWordType;
 }
 export type MarkdownLine = MarkdownWord[];
+/** Returns `true` if the line fits a constraint (e.g. it's under 𝑛 chars) */
 export type CheckFitFunction = (text: MarkdownLine) => boolean;