Check the performance of the initial character string

when writing a function today, You need to determine whether a string is an XML or a number. When you start with startswith, you can determine whether the string starts with startswith. Later, you find that this function requires high-frequency calls, I don't know if startswith has performance problems. The following Code is written for verification:

 var content =  "
   
     1 
   " ; stopwatch Sw = stopwatch. startnew ();  for  ( int  I = 0; I <1000000; I ++) {var r = content. startswith ( "<" );} SW. stop (); console. writeline ( "Test 1:"  + SW. elapsedmilliseconds); Sw = stopwatch. startnew ();  for  ( int  I = 0; I <1000000; I ++) {var r = content. startswith ( "
   
    " 
   );} SW. stop (); console. writeline ( "Test 2:"  + SW. elapsedmilliseconds); Sw = stopwatch. startnew ();  for  ( int  I = 0; I <1000000; I ++) {var r = content [0] =  ';} SW. stop (); console. writeline ( "Test 3:"  + SW. elapsedmilliseconds); 

Basically, the first three types of performance are the highest, but the second type should be safe.