Regular expression parser (regexp_parser)

1.2

The project implements the C++ parser class base_parsers::basic_regexp_parser usable for finding the matching sequence in the input using regular expression. The regular expression pattern is a parameter in parsers constructor. Also allows to retrieve subexpressions matches in few steps. Supports wide chars.

The recognition of the pattern and finding of the input matches accomplishes The Open Group specification Issue 6, IEEE Std 1003.1, 2004 Edition, Copyright 2001-2004 The IEEE and The Open Group

There are two specializations of the base_parsers::basic_regexp_parser template class - one for char (regexp_parser) and one for wchar_t (wregexp_parser) input type.

To use regexp_parser in your project, copy/extract all include files from ./src/base_parsers and ./src/regexp_parsers into include directory accessible from your project, include the regexp_parser.h file and use it, for example, in following manner:

regexp_parser rxp( "(^wee|^week)(knights|night)" );

If regexp pattern comes also from user input, it is possible to check the pattern:

if( !rxp.is_pattern_valid() )
{
        cerr << "invalid pattern" << endl;
}

To parse the input (find the matching part), simply call parse() method

string input = "helloweeknights";
rxp.parse( input.c_str, input.length() );
if( rxp.is_parsed() )
{
        cout << "input part recognized by (^wee|^week)(knights|night) on position ";
        cout rxp.recognized_position() << "with size=" << rxp.recognized_size() << endl;
        // output is: 
        // input part recognized by (^wee|^week)(knights|night) on position 5 with size=10
}
else
{
        cout << "input not recognized by (^wee|^week)(knights|night)" << endl;two
}

The parser is also capable to return matches of the regexp and to address all subexpressions matches. Each subexpression is addressed by a key in dotted form. In the match key, the number specifies the subexpression position. By '.' are separated levels, if subexpressions are submerged i.e. "(a)" can be addressed by 1.1, "((a))" by 1.1.1 etc.
By number is specified the subexpression position on the level. Suppose we have pattern "a(a(b){1,3})" and input "aaabbbb". Now we are interested in subexression 1.1.2 = second b

regexp_parser rxp("a(a(b){1,3})");
rxp.parse( "aaabbbb", 7 );

matches m;
rxp.assign_matches(m);
match subexpr = m.get("1.1.2");
if( subexpr.is_valid() )
{
        ulong pos = subexpr.get_pos();  // == 4
        ulong size = subexpr.get_size();// == 1 
        // do some work
}

To iterate through all matches, it is possible to use method get_all().

matches::matches_coll mc;
m.get_all(mc);
matches::matches_coll::iterator it = mc.begin();
while( it != mc.end() )
{
        cout << "    match (subexpr) key = " <<  (*it).first << "  position=";
        cout << (*it).second.get_pos() << " size=" << (*it).second.get_size();
        cout << "; " << endl;
        it++;
}

Note for developers:
To test regular pattern recognition (not finding the matches, at least not in this version), it is possible to use tracer in ./src/common directory. But to be honest, I never used that (produces too much traces).

// when using this directove, the ./src/common/tracer.h must be included
#define TRACE
.
.
.
// switch the trace on
parsers_common::trace_context::get().trace_on();
// will trace regexp recognition (or by other words, building the parsing engine).
regexp_parser rxp("a(a(b){1,3})");
// switch the trace off
parsers_common::trace_context::get().trace_off();

With use of matches it is possible to manipulate the input string. See also regexp_test.cpp in test directory.

Following are test results from regexp_parser tests:

[--8z--] parsed succesfully input = - recognized succesfully
[[.-.]] parsed succesfully input = - recognized succesfully
[a-bc] parsed succesfully input = ch recognized succesfully
[[:print:]] parsed succesfully input = 1 recognized succesfully
[8--] parsed succesfully input = - recognized succesfully
[a-c] parsed succesfully input = a recognized succesfully
[^a-f] parsed succesfully input = g recognized succesfully
[^a-f] parsed succesfully input = c not recognized succesfully
[[:alnum:]] parsed succesfully input = a recognized succesfully
[--z] parsed succesfully input = - recognized succesfully
[aa-b] parsed succesfully input = b recognized succesfully
[a-bc-h] parsed succesfully input = g recognized succesfully
[a-bc-de-f] parsed succesfully input = a recognized succesfully
[[.a.]] parsed succesfully input = a recognized succesfully
[[=a=]] parsed succesfully input = a recognized succesfully
[[.ch.]] parsed succesfully input = ch not recognized wrongly
  "abc "def" "ghi" jkl" succesfully recognized by "".*"" ,size=11 position=4
    match (subexpr) key = 1  position=4 size=11;

  "abc "def" "ghi" jkl" succesfully recognized by "".*?"" ,size=5 position=4
    match (subexpr) key = 1  position=4 size=5;

  "aaabbbb" succesfully recognized by "a(a(b){1,3})" ,size=6 position=0
    match (subexpr) key = 1  position=0 size=6;
    match (subexpr) key = 1.1  position=1 size=5;
    match (subexpr) key = 1.1.1  position=3 size=1;
    match (subexpr) key = 1.1.2  position=4 size=1;
    match (subexpr) key = 1.1.3  position=5 size=1;

  "abab" succesfully recognized by "(ab){2,5}" ,size=4 position=0
    match (subexpr) key = 1  position=0 size=4;
    match (subexpr) key = 1.1  position=0 size=2;
    match (subexpr) key = 1.2  position=2 size=2;

  "ab" succesfully not recognized by "(ab){2,5}"
  "aa" succesfully recognized by "(a){2}" ,size=2 position=0
    match (subexpr) key = 1  position=0 size=2;
    match (subexpr) key = 1.1  position=0 size=1;
    match (subexpr) key = 1.2  position=1 size=1;

  "a" succesfully recognized by "(a){1}" ,size=1 position=0
    match (subexpr) key = 1  position=0 size=1;
    match (subexpr) key = 1.1  position=0 size=1;

  "aa" succesfully recognized by "((a){1,2}){2}" ,size=2 position=0
    match (subexpr) key = 1  position=0 size=2;
    match (subexpr) key = 1.1  position=0 size=1;
    match (subexpr) key = 1.1.1  position=0 size=1;
    match (subexpr) key = 1.2  position=1 size=1;
    match (subexpr) key = 1.2.1  position=1 size=1;

  "abcabcabc" succesfully recognized by "((abc){1,3}){2,5}" ,size=9 position=0
    match (subexpr) key = 1  position=0 size=9;
    match (subexpr) key = 1.1  position=0 size=6;
    match (subexpr) key = 1.1.1  position=0 size=3;
    match (subexpr) key = 1.1.2  position=3 size=3;
    match (subexpr) key = 1.2  position=6 size=3;
    match (subexpr) key = 1.2.1  position=6 size=3;

  "abcabcabcabcabcabcabcabc" succesfully recognized by "(((abc){2,5}){2,5}){2,5}" ,size=24 position=0
    match (subexpr) key = 1  position=0 size=24;
    match (subexpr) key = 1.1  position=0 size=12;
    match (subexpr) key = 1.1.1  position=0 size=6;
    match (subexpr) key = 1.1.1.1  position=0 size=3;
    match (subexpr) key = 1.1.1.2  position=3 size=3;
    match (subexpr) key = 1.1.2  position=6 size=6;
    match (subexpr) key = 1.1.2.1  position=6 size=3;
    match (subexpr) key = 1.1.2.2  position=9 size=3;
    match (subexpr) key = 1.2  position=12 size=12;
    match (subexpr) key = 1.2.1  position=12 size=6;
    match (subexpr) key = 1.2.1.1  position=12 size=3;
    match (subexpr) key = 1.2.1.2  position=15 size=3;
    match (subexpr) key = 1.2.2  position=18 size=6;
    match (subexpr) key = 1.2.2.1  position=18 size=3;
    match (subexpr) key = 1.2.2.2  position=21 size=3;

  "abcabcabcabcabcabcabc" succesfully not recognized by "(((abc){2,5}){2,5}){2,5}"
  "aaaa" succesfully recognized by "(a)*" ,size=4 position=0
    match (subexpr) key = 1  position=0 size=4;
    match (subexpr) key = 1.1  position=0 size=1;
    match (subexpr) key = 1.2  position=1 size=1;
    match (subexpr) key = 1.3  position=2 size=1;
    match (subexpr) key = 1.4  position=3 size=1;

  "abbbc" succesfully recognized by "bb*" ,size=3 position=1
    match (subexpr) key = 1  position=1 size=3;

  "cdabababb" succesfully recognized by "[ab]*" ,size=7 position=2
    match (subexpr) key = 1  position=2 size=7;

  "abcabcabc" succesfully recognized by "(abc){1,3}" ,size=9 position=0
    match (subexpr) key = 1  position=0 size=9;
    match (subexpr) key = 1.1  position=0 size=3;
    match (subexpr) key = 1.2  position=3 size=3;
    match (subexpr) key = 1.3  position=6 size=3;

  "cabc" succesfully recognized by "(abc){1,3}" ,size=4 position=0
    match (subexpr) key = 1  position=0 size=4;
    match (subexpr) key = 1.1  position=1 size=3;

  "cabcddcabd" succesfully recognized by "(abc)(cab)d{1,3}" ,size=10 position=0
    match (subexpr) key = 1  position=0 size=10;
    match (subexpr) key = 1.1  position=1 size=3;
    match (subexpr) key = 1.2  position=6 size=3;

  "cabcddcabddddd" succesfully recognized by "(abc)(cab)d{1,3}" ,size=12 position=0
    match (subexpr) key = 1  position=0 size=12;
    match (subexpr) key = 1.1  position=1 size=3;
    match (subexpr) key = 1.2  position=6 size=3;

  "ddddd" succesfully recognized by "d{1,3}d{2,5}" ,size=5 position=0
    match (subexpr) key = 1  position=0 size=5;

  "ddddd" succesfully recognized by "d{1,3}" ,size=3 position=0
    match (subexpr) key = 1  position=0 size=3;

  "abcabcabcabc" succesfully recognized by "((abc){1,2}){2,5}" ,size=12 position=0
    match (subexpr) key = 1  position=0 size=12;
    match (subexpr) key = 1.1  position=0 size=6;
    match (subexpr) key = 1.1.1  position=0 size=3;
    match (subexpr) key = 1.1.2  position=3 size=3;
    match (subexpr) key = 1.2  position=6 size=6;
    match (subexpr) key = 1.2.1  position=6 size=3;
    match (subexpr) key = 1.2.2  position=9 size=3;

  "abcabcabcabc" succesfully recognized by "(abc){1,2}{2}" ,size=12 position=0
    match (subexpr) key = 1  position=0 size=12;
    match (subexpr) key = 1.1  position=0 size=3;
    match (subexpr) key = 1.2  position=3 size=3;
    match (subexpr) key = 1.3  position=6 size=3;
    match (subexpr) key = 1.4  position=9 size=3;

  "caabcbdcb" succesfully recognized by "a(a(b){3})" ,size=8 position=1
    match (subexpr) key = 1  position=1 size=8;
    match (subexpr) key = 1.1  position=2 size=7;
    match (subexpr) key = 1.1.1  position=3 size=1;
    match (subexpr) key = 1.1.2  position=5 size=1;
    match (subexpr) key = 1.1.3  position=8 size=1;

  "ba" succesfully not recognized by "^a$"
  "a" succesfully recognized by "^a$" ,size=1 position=0
    match (subexpr) key = 1  position=0 size=1;

  "bac" succesfully not recognized by "^a$"
  "abc" succesfully not recognized by "^a$"
  "aaa" succesfully recognized by "^aaa$" ,size=3 position=0
    match (subexpr) key = 1  position=0 size=3;

  "aba" succesfully recognized by "^a(a)$" ,size=3 position=0
    match (subexpr) key = 1  position=0 size=3;
    match (subexpr) key = 1.1  position=2 size=1;

  "abbbaa" succesfully recognized by "^a(a)a$" ,size=6 position=0
    match (subexpr) key = 1  position=0 size=6;
    match (subexpr) key = 1.1  position=4 size=1;

  "abbaccb" succesfully recognized by "^a(a(b))$" ,size=7 position=0
    match (subexpr) key = 1  position=0 size=7;
    match (subexpr) key = 1.1  position=3 size=4;
    match (subexpr) key = 1.1.1  position=6 size=1;

  "b" succesfully recognized by "a|b" ,size=1 position=0
    match (subexpr) key = 1  position=0 size=1;

  "ab" succesfully recognized by "(a)(b)" ,size=2 position=0
    match (subexpr) key = 1  position=0 size=2;
    match (subexpr) key = 1.1  position=0 size=1;
    match (subexpr) key = 1.2  position=1 size=1;

  "a" succesfully recognized by "(a)|(b)" ,size=1 position=0
    match (subexpr) key = 1  position=0 size=1;
    match (subexpr) key = 1.1  position=0 size=1;

  "add" succesfully recognized by "(a)|(b)|c|dd" ,size=2 position=1
    match (subexpr) key = 1  position=1 size=2;

  "ac" succesfully recognized by "(a)(b|c)" ,size=2 position=0
    match (subexpr) key = 1  position=0 size=2;
    match (subexpr) key = 1.1  position=0 size=1;
    match (subexpr) key = 1.2  position=1 size=1;

  "ac" succesfully recognized by "(a|b)(c|d)" ,size=2 position=0
    match (subexpr) key = 1  position=0 size=2;
    match (subexpr) key = 1.1  position=0 size=1;
    match (subexpr) key = 1.2  position=1 size=1;

  "aic" succesfully recognized by "(ai|b)(c|d)" ,size=3 position=0
    match (subexpr) key = 1  position=0 size=3;
    match (subexpr) key = 1.1  position=0 size=2;
    match (subexpr) key = 1.2  position=2 size=1;

  "abbaba" succesfully recognized by "^a(a(^b)a$)" ,size=6 position=0
    match (subexpr) key = 1  position=0 size=6;
    match (subexpr) key = 1.1  position=3 size=3;
    match (subexpr) key = 1.1.1  position=4 size=1;

  "weeknights" succesfully recognized by "(wee|week)(knights|night)" ,size=10 position=0
    match (subexpr) key = 1  position=0 size=10;
    match (subexpr) key = 1.1  position=0 size=3;
    match (subexpr) key = 1.2  position=3 size=7;

  "aabcbdcb" succesfully recognized by "^a(a(b){3})$" ,size=8 position=0
    match (subexpr) key = 1  position=0 size=8;
    match (subexpr) key = 1.1  position=1 size=7;
    match (subexpr) key = 1.1.1  position=2 size=1;
    match (subexpr) key = 1.1.2  position=4 size=1;
    match (subexpr) key = 1.1.3  position=7 size=1;

  "abab" succesfully recognized by "(ab){2,5}" ,size=4 position=0
    match (subexpr) key = 1  position=0 size=4;
    match (subexpr) key = 1.1  position=0 size=2;
    match (subexpr) key = 1.2  position=2 size=2;

  "ab" succesfully not recognized by "(ab){2,5}"
  "aa" succesfully recognized by "(a){2}" ,size=2 position=0
    match (subexpr) key = 1  position=0 size=2;
    match (subexpr) key = 1.1  position=0 size=1;
    match (subexpr) key = 1.2  position=1 size=1;

  "a" succesfully recognized by "(a){1}" ,size=1 position=0
    match (subexpr) key = 1  position=0 size=1;
    match (subexpr) key = 1.1  position=0 size=1;

  "aa" succesfully recognized by "((a){1,2}){2}" ,size=2 position=0
    match (subexpr) key = 1  position=0 size=2;
    match (subexpr) key = 1.1  position=0 size=1;
    match (subexpr) key = 1.1.1  position=0 size=1;
    match (subexpr) key = 1.2  position=1 size=1;
    match (subexpr) key = 1.2.1  position=1 size=1;

  "abcabcabc" succesfully recognized by "((abc){1,3}){2,5}" ,size=9 position=0
    match (subexpr) key = 1  position=0 size=9;
    match (subexpr) key = 1.1  position=0 size=6;
    match (subexpr) key = 1.1.1  position=0 size=3;
    match (subexpr) key = 1.1.2  position=3 size=3;
    match (subexpr) key = 1.2  position=6 size=3;
    match (subexpr) key = 1.2.1  position=6 size=3;

  "abcabcabcabcabcabcabcabc" succesfully recognized by "(((abc){2,5}){2,5}){2,5}" ,size=24 position=0
    match (subexpr) key = 1  position=0 size=24;
    match (subexpr) key = 1.1  position=0 size=12;
    match (subexpr) key = 1.1.1  position=0 size=6;
    match (subexpr) key = 1.1.1.1  position=0 size=3;
    match (subexpr) key = 1.1.1.2  position=3 size=3;
    match (subexpr) key = 1.1.2  position=6 size=6;
    match (subexpr) key = 1.1.2.1  position=6 size=3;
    match (subexpr) key = 1.1.2.2  position=9 size=3;
    match (subexpr) key = 1.2  position=12 size=12;
    match (subexpr) key = 1.2.1  position=12 size=6;
    match (subexpr) key = 1.2.1.1  position=12 size=3;
    match (subexpr) key = 1.2.1.2  position=15 size=3;
    match (subexpr) key = 1.2.2  position=18 size=6;
    match (subexpr) key = 1.2.2.1  position=18 size=3;
    match (subexpr) key = 1.2.2.2  position=21 size=3;

  "abcabcabcabcabcabcabc" succesfully not recognized by "(((abc){2,5}){2,5}){2,5}"
  "aaaa" succesfully recognized by "(a)*" ,size=4 position=0
    match (subexpr) key = 1  position=0 size=4;
    match (subexpr) key = 1.1  position=0 size=1;
    match (subexpr) key = 1.2  position=1 size=1;
    match (subexpr) key = 1.3  position=2 size=1;
    match (subexpr) key = 1.4  position=3 size=1;

  "abbbc" succesfully recognized by "bb*" ,size=3 position=1
    match (subexpr) key = 1  position=1 size=3;

  "cdabababb" succesfully recognized by "[ab]*" ,size=7 position=2
    match (subexpr) key = 1  position=2 size=7;

  "abcabcabc" succesfully recognized by "(abc){1,3}" ,size=9 position=0
    match (subexpr) key = 1  position=0 size=9;
    match (subexpr) key = 1.1  position=0 size=3;
    match (subexpr) key = 1.2  position=3 size=3;
    match (subexpr) key = 1.3  position=6 size=3;

  "cabc" succesfully recognized by "(abc){1,3}" ,size=4 position=0
    match (subexpr) key = 1  position=0 size=4;
    match (subexpr) key = 1.1  position=1 size=3;

  "cabcddcabd" succesfully recognized by "(abc)(cab)d{1,3}" ,size=10 position=0
    match (subexpr) key = 1  position=0 size=10;
    match (subexpr) key = 1.1  position=1 size=3;
    match (subexpr) key = 1.2  position=6 size=3;

  "cabcddcabddddd" succesfully recognized by "(abc)(cab)d{1,3}" ,size=12 position=0
    match (subexpr) key = 1  position=0 size=12;
    match (subexpr) key = 1.1  position=1 size=3;
    match (subexpr) key = 1.2  position=6 size=3;

  "ddddd" succesfully recognized by "d{1,3}d{2,5}" ,size=5 position=0
    match (subexpr) key = 1  position=0 size=5;

  "ddddd" succesfully recognized by "d{1,3}" ,size=3 position=0
    match (subexpr) key = 1  position=0 size=3;

  "abcabcabcabc" succesfully recognized by "((abc){1,2}){2,5}" ,size=12 position=0
    match (subexpr) key = 1  position=0 size=12;
    match (subexpr) key = 1.1  position=0 size=6;
    match (subexpr) key = 1.1.1  position=0 size=3;
    match (subexpr) key = 1.1.2  position=3 size=3;
    match (subexpr) key = 1.2  position=6 size=6;
    match (subexpr) key = 1.2.1  position=6 size=3;
    match (subexpr) key = 1.2.2  position=9 size=3;

  "abcabcabcabc" succesfully recognized by "(abc){1,2}{2}" ,size=12 position=0
    match (subexpr) key = 1  position=0 size=12;
    match (subexpr) key = 1.1  position=0 size=3;
    match (subexpr) key = 1.2  position=3 size=3;
    match (subexpr) key = 1.3  position=6 size=3;
    match (subexpr) key = 1.4  position=9 size=3;

  "caabcbdcb" succesfully recognized by "a(a(b){3})" ,size=8 position=1
    match (subexpr) key = 1  position=1 size=8;
    match (subexpr) key = 1.1  position=2 size=7;
    match (subexpr) key = 1.1.1  position=3 size=1;
    match (subexpr) key = 1.1.2  position=5 size=1;
    match (subexpr) key = 1.1.3  position=8 size=1;

  "ba" succesfully not recognized by "^a$"
  "a" succesfully recognized by "^a$" ,size=1 position=0
    match (subexpr) key = 1  position=0 size=1;

  "bac" succesfully not recognized by "^a$"
  "abc" succesfully not recognized by "^a$"
  "aaa" succesfully recognized by "^aaa$" ,size=3 position=0
    match (subexpr) key = 1  position=0 size=3;

  "aba" succesfully recognized by "^a(a)$" ,size=3 position=0
    match (subexpr) key = 1  position=0 size=3;
    match (subexpr) key = 1.1  position=2 size=1;

  "abbbaa" succesfully recognized by "^a(a)a$" ,size=6 position=0
    match (subexpr) key = 1  position=0 size=6;
    match (subexpr) key = 1.1  position=4 size=1;

  "abbaccb" succesfully recognized by "^a(a(b))$" ,size=7 position=0
    match (subexpr) key = 1  position=0 size=7;
    match (subexpr) key = 1.1  position=3 size=4;
    match (subexpr) key = 1.1.1  position=6 size=1;

  "b" succesfully recognized by "a|b" ,size=1 position=0
    match (subexpr) key = 1  position=0 size=1;

  "ab" succesfully recognized by "(a)(b)" ,size=2 position=0
    match (subexpr) key = 1  position=0 size=2;
    match (subexpr) key = 1.1  position=0 size=1;
    match (subexpr) key = 1.2  position=1 size=1;

  "a" succesfully recognized by "(a)|(b)" ,size=1 position=0
    match (subexpr) key = 1  position=0 size=1;
    match (subexpr) key = 1.1  position=0 size=1;

  "ca" succesfully recognized by "a|b" ,size=1 position=1
    match (subexpr) key = 1  position=1 size=1;

  "ca" succesfully recognized by "(a)|(b)" ,size=2 position=0
    match (subexpr) key = 1  position=0 size=2;
    match (subexpr) key = 1.1  position=1 size=1;

  "ca" succesfully recognized by "(^a)|(b)" ,size=1 position=1
    match (subexpr) key = 1  position=1 size=1;
    match (subexpr) key = 1.1  position=1 size=1;

  "ca" succesfully recognized by "(a)" ,size=2 position=0
    match (subexpr) key = 1  position=0 size=2;
    match (subexpr) key = 1.1  position=1 size=1;

  "ca" succesfully recognized by "(^a)" ,size=1 position=1
    match (subexpr) key = 1  position=1 size=1;
    match (subexpr) key = 1.1  position=1 size=1;

  "add" succesfully recognized by "(a)|(b)|c|dd" ,size=2 position=1
    match (subexpr) key = 1  position=1 size=2;

  "ac" succesfully recognized by "(a)(b|c)" ,size=2 position=0
    match (subexpr) key = 1  position=0 size=2;
    match (subexpr) key = 1.1  position=0 size=1;
    match (subexpr) key = 1.2  position=1 size=1;

  "ac" succesfully recognized by "(a|b)(c|d)" ,size=2 position=0
    match (subexpr) key = 1  position=0 size=2;
    match (subexpr) key = 1.1  position=0 size=1;
    match (subexpr) key = 1.2  position=1 size=1;

  "aic" succesfully recognized by "(ai|b)(c|d)" ,size=3 position=0
    match (subexpr) key = 1  position=0 size=3;
    match (subexpr) key = 1.1  position=0 size=2;
    match (subexpr) key = 1.2  position=2 size=1;

  "abbaba" succesfully recognized by "^a(a(^b)a$)" ,size=6 position=0
    match (subexpr) key = 1  position=0 size=6;
    match (subexpr) key = 1.1  position=3 size=3;
    match (subexpr) key = 1.1.1  position=4 size=1;

  "weeknights" succesfully recognized by "(wee|week)(knights|night)" ,size=10 position=0
    match (subexpr) key = 1  position=0 size=10;
    match (subexpr) key = 1.1  position=0 size=3;
    match (subexpr) key = 1.2  position=3 size=7;

  "helloweeknights" succesfully recognized by "o(wee|week)(knights|night)" ,size=11 position=4
    match (subexpr) key = 1  position=4 size=11;
    match (subexpr) key = 1.1  position=5 size=3;
    match (subexpr) key = 1.2  position=8 size=7;

  "helloweeknights" succesfully recognized by "(wee|week)(knights|night)" ,size=15 position=0
    match (subexpr) key = 1  position=0 size=15;
    match (subexpr) key = 1.1  position=5 size=3;
    match (subexpr) key = 1.2  position=8 size=7;

  "helloweeknights" succesfully recognized by "(^wee|^week)(knights|night)" ,size=10 position=5
    match (subexpr) key = 1  position=5 size=10;
    match (subexpr) key = 1.1  position=5 size=3;
    match (subexpr) key = 1.2  position=8 size=7;

  "aabcbdcb" succesfully recognized by "^a(a(b){3})$" ,size=8 position=0
    match (subexpr) key = 1  position=0 size=8;
    match (subexpr) key = 1.1  position=1 size=7;
    match (subexpr) key = 1.1.1  position=2 size=1;
    match (subexpr) key = 1.1.2  position=4 size=1;
    match (subexpr) key = 1.1.3  position=7 size=1;

---