Operator += appends single-argument values, including initializer lists of characters since C++11.
append() is overloaded for different arguments. One version of append() lets you append a range
of characters specified by two iterators (see Section 13.2.14, page 684). The push_back() member
function is provided for back inserters so that STL algorithms are able to append characters to a
string (see Section 9.4.2, page 455, for details about back inserters and Section 13.2.14, page 688,
for an example of their use with strings).
Similar to append(), several insert() member functions enable you to insert characters.
These functions require the index of the character, after which the new characters are inserted: