List of steps to reproduce (step by step, including full links if applicable):
Start a blank page :-

Enter the following code extract

<score>
\header { tagline = ##f title = \markup { "A Mighty Fortress is Our God" "         " "121" } subsubtitle = "(EIN' FESTE BURG. 8,7,8,7,6,6,6,6,7)" composer = "Martin Luther, 1529" poet = \markup { \center-column { "Martin Luther, 1529" "Translated by Frederick H. Hedge, 1853" } } }
</score>

Preview the example.

What happens?:

Example code will fail to render , generating a "unknown escaped string: `\center-column' " error.

What should have happened instead?:

The example should have generated a visible header with the relevant poem field formatted with a centered column.

Software version (if not a Wikimedia wiki), browser information, screenshots, other information, etc:

Windows 7, Firefox 93.0a1 (2021-08-20)