elaborate on the effect of '?' on README

README.md

@@ -28,6 +28,7 @@ Note that `{}` extracts positional arguments after the string sequentially (the
 You can use `{:spec}` to customize your output. See the Rust docs linked above for more info, but here's a summary:
 
 - Adding a `?` at the end of `spec` (that is, writing e.g. `{0:?}`) will call `repr()` to stringify your argument, instead of `str()`. Note that this only has an effect if your argument is a string, an integer, a float or a `label()` / `<label>` - for all other types (such as booleans or elements), `repr()` is always called (as `str()` is unsupported for those).
+    - For strings, `?` (and thus `repr()`) has the effect of printing them with double quotes. For floats, this ensures a `.0` appears after it, even if it doesn't have decimal digits. For integers, this doesn't change anything. Finally, for labels, the `<label>` (with `?`) is printed as `<label>` instead of `label`.
 - After the `:`, add e.g. `_<8` to align the string to the left, padding it with as many `_`s as necessary for it to be at least `8` characters long. Replace `<` by `>` for right alignment, or `^` for center alignment. (If the `_` is omitted, it defaults to ' ' (aligns with spaces).)
     - If you prefer to specify the minimum width (the `8` there) as a separate argument to `strfmt` instead, you can specify `argument$` in place of the width, which will extract it from the integer at `argument`. For example, `_^3$` will center align the output with `_`s, where the minimum width desired is specified by the fourth positional argument (index `3`), as an integer. This means that a call such as `strfmt("{:_^3$}", 1, 2, 3, 4)` would produce `"__1__"`, as `3$` would evaluate to `4` (the value at the fourth positional argument/index `3`). Similarly, `named$` would take the width from the argument with name `named`, if it is an integer (otherwise, error).
 - For numbers: