what exactly is string length?

[mw]

On Friday, 2 April 2021 at 04:38:37 UTC, mw wrote:
> On Friday, 2 April 2021 at 04:36:01 UTC, rikki cattermole wrote:
> I don't get it, what do you mean by the assertion:
>
>
> assert(t[9] == '\0');
>
>
> t == "head-abc-tail"

Just tried this:

https://run.dlang.io/is/SFU5p4

```
import std;
import std.conv : text;


void main()
{
     char[6] s;
     s = "abc";
     writeln(s, s.length);  // abc6, ok it's the static array's 
length

     string t = text("head-", s, "-tail");
     writeln(t, t.length);  // head-abc-tail16, why 16 instead of 
13, t's type is string here
     assert(t[9] == '\0');   // ok
     assert(t == "head-abc-tail");  // failed!
}
```

I'm even more puzzled by the last 2 assertions behavior: t is 
print out as "head-abc-tail".