Parameters of child block are available for editing while editing parent block - in Block Editor.
However, seems that I cannot enter an expression as value for (child) block parameter in (child) block properties table - I would like to use an expression which references a parameter in the parent block to set child block parameter value.
In summary:
Am I correct in saying that I cannot enter an expression as value for (child) block parameter in (child) block properties table. (I dont wish to get involved with automation for this purpose at this time.)