Using C++14 digit separators, the CPP semantic analysis reports an error:

Ex:
    if ( value > 100'000'000'000'000'000ll) {
        suffix = "P";
        if (isSet(fmt, xfmt::round))
            value +=   500'000'000'000'000ll;
        value /= 1'000'000'000'000'000ll;
    } else if ( value > 100'000'000'000'000ll) {
        suffix = "T";
        if (isSet(fmt, xfmt::round))
            value +=   500'000'000'000ll;
        value /= 1'000'000'000'000ll;
    } else if ( value > 100'000'000'000ll) {

Hovering over the 'if' line, the pop-up says:
 "Problem in semantic analysis
  Location: ...
  Expected ')'..."

Hovering over the first "value += ..." I get:
 "expected ';' after expression."

Hovering over the second else-if:
  "Missing terminating ' character"