begin method
Called when the beginning of a tag is encountered.
Implementation
@override
void begin(TagContext tc, String data) {
final argInfo = ArgInfo(tc, data, stringFirst: false);
final parentArgs = tc.parent?.args;
var var1 = parentArgs != null ?
(parentArgs[argInfo.first] = tc.nextVar()): argInfo.first,
var2 = tc.nextVar();
tc..push(var1)..push(var2);
if (tc.parent?.args == null) var1 = "_${var1}_";
tc.writeln("\n${tc.pre}final $var1 = StringBuffer(), $var2 = connect;${tc.getLineNumberComment()}\n"
"${tc.pre}connect = HttpConnect.stringBuffer(connect, $var1); response = connect.response;");
}