How to mark EditableGrid Header in BOLD

There's currently no way to do *exactly* this (edit: David has provided a neat workaround below, which might work for you).  Column headers for both types of grid are only able to use their built-in formatting.

I agree it might be nice if the grid header function was updated to accept a a!richTextItem() object instead of just plaintext, which would open up some fun new possibilities, but I don't expect this is even on Appian's priority radar at the moment.

Unicode bold letters start at 119808.

So char(119808) should render a capital A in bold.  code("A") gives you 65.  So, you need to add 119743 to each of your letters to make them bold.  Unless they're spaces or punctuation.

This gets you ALL CAPS, but the lower case letters aren't in the same relative position on both ends of the unicode standard.  So you have to adjust the starting point for the list of lowercase letters, and the number you have to add.

joinarray(
  a!forEach(
    items: code(ri!text),
    expression: if(
      and(fv!item > 64, fv!item < 91),
      char(fv!item + 119743),
      if(
        and(fv!item > 96, fv!item < 123),
        char(fv!item + 119737),
        char(fv!item)
      )
    )
  )
)