what exactly is string length?

[mw]

On Friday, 2 April 2021 at 04:36:01 UTC, rikki cattermole wrote:
> On 02/04/2021 5:32 PM, mw wrote:
>> ---
>> 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?
> assert(t[9] == '\0');
>> }
>> ---

I don't get it, what do you mean by the assertion:


assert(t[9] == '\0');


t == "head-abc-tail"