Appends the value
to the previous value of attribute name
.
If the attribute was not present, it will just set the attribute name
to
value
. Otherwise, it will use the separator
to put between the
previous value and value
.
If separator
is not specified or null
, a single space will be
used as separator.
Throws an ArgumentError
if name
or value
is null
.
Source
void append(String name, String value, {String separator});