Update index.md

Co-authored-by: Johannes Soltwedel <38459088+jo-mueller@users.noreply.github.com>

Author: will-moore

index.md

@@ -460,7 +460,7 @@ The following transformations are supported:
 | [`displacements`](#coordinates-displacements-md) | `"path":str` | Displacement field transformation located at `path`. |
 | [`coordinates`](#coordinates-displacements-md) | `"path":str` | Coordinate field transformation located at `path`. |
 | [`bijection`](#bijection-md) | `"forward":Transformation`<br>`"inverse":Transformation` | An invertible transformation providing an explicit forward transformation and its inverse. |
-| [`byDimension`](#bydimension-md) | `"transformations":List[Transformation]`.<br>Tranformations in the array must have<br>`"input_axes": List[number]`, <br> and `"output_axes": List[number]` | A high dimensional transformation using lower dimensional transformations on subsets of dimensions. |
+| [`byDimension`](#bydimension-md) | `"transformations":List[Transformation]`.<br>Transformations in the array MUST have<br>`"input_axes": List[number]`, <br> and `"output_axes": List[number]` | A high dimensional transformation using lower dimensional transformations on subsets of dimensions. |
 
 Implementations SHOULD prefer to store transformations as a sequence of less expressive transformations where possible
 (e.g., sequence[translation, rotation], instead of affine transformation with translation/rotation).