[texhax] \overline and \phantom

[Heiko Oberdiek]

On Mon, Jul 30, 2012 at 07:47:35PM +0100, Paul Stanley wrote:

> does the below code draw a line whose length equals the length of
> the expression a+x and whose height is equal to or greater than the
> x height of the tallest glyph in the expression?

> $\overline{\phantom{a+x}}$

>From "The TeXbook" for \overline:

| The \sqrt and \underline and \overline operations are able to place
| lines above or below subformulas of any size or shape; the bar lines
| change their size and position, so that they are long enough to
| cover the subformula, and high enough or low enough not to bump
| into it. [...]

>From "The Texbook" for \phantom:

| If you say `\phantom{<subformula>}' in any formula, plain TeX
| will do its spacing as if you had said simply `{<subformula>}',
| but the subformula itself will be invisible. [...]

Therefore, the length and the tallest glyph do matter for \overline.

Yours sincerely
  Heiko Oberdiek