Before you invest your time sutdying this topic, I suggest you start out with the recursion summary on the main syntax page. Is it ok if I translate these two excellent article into chinese? Then In a nested loop, we enumerate all the Capture instances. This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. I'm going to show you how to do something with regular expressions that's long been thought impossible. Would I have the hornor to translate them into Chinese and publish them on. Set containing “[” and the letters “a” to “z” Match Nested Brackets with Regex: A new approach My first blog post was a bit of a snoozefest, so I feel I ought to make this one a little shorter and more to the point. The regex engine advances to (?'between-open'c). forcing a negative lookahead with no expression, which will always fail. So i thought i could type this article into it, and get an result. (? The expression is encapsulated in a parenthesis, and therefore the RegEx engine will capture this part of the source into a group numbered 1. This is quite interesting - so let's dig a bit deeper into it. He and I are both working a lot in Behat, which relies heavily on regular expressions to map human-like sentences to PHP code.One of the common patterns in that space is the quoted-string, which is a fantastic … The fundamentals: Named captures Even though this is not a new feature, named captures are fundamental for understanding the nested constructions in.NET regular expressions. Let's see some code. This crate can handle both untrusted regular expressions and untrusted search text. Bl00d_b0b (Edvard Filistovic) February 4, 2020, 1:08pm You can download it free from http://www.codeproject.com/KB/string/regextester.aspx and http://sourceforge.net/projects/regextester, Hi, Morten, your articles are great! I found the article useful, but frustrating because there were some omissions and errors. If there were no nested tags then this regular expression would be rather simple but since there are one essentially needs to wrap the expression from above with the set of outer tags and then capture the inner text. For the following strings, write an expression that matches and captures both the full date, as well as the … The class is a specific .NET invention and even though many developers won't ever need to call this class explicitly, it does have some cool features, for example with nested constructions. Example. Im very new to Regex., an i downloaded Expresso to help me test some basic Regex. When alternation occurs, the .NET RegEx engine will try out the matches one at a time accepting the first match - even if this is not the longest match. The invention of an auxiliary stack in the .NET RegEx engine has made it possible to match nested constructions and keep track of the matches bringing even more power to regular expressions. 'between-open'c)+ to the string ooccc. The Capture class is an essential part of the Regex class. Regex Tester requires a modern browser. Workarounds There are two main workarounds to the lack of support for variable-width (or infinite-width) lookbehind: Capture … Basic Capture Groups. In the previous chapter parenthesis were used to capture a … The version of the regular expression that uses the * greedy quantifier is \b.*([0-9]{4})\b. 'open'o) matches the first o and stores that as the first capture of the group “open”. Here we've also used named capturing, but we don't just capture an empty string, we are capturing the letter a onto the stack A and the letter b onto the stack B. To only capture 3 as in Java, you would have to make the quantifier lazy: (? Literal Parentheses When reversing, Django will try to fill in all outer captured arguments, ignoring any nested captured arguments. When the RegEx engine matches a
(line 3), it is at the same time told to match something else: (?). Regexp is a more natural abbreviation than regex, but is harder to pronounce. This Framework provides a basis for understanding how the .NET RegEx engine is capable of matching nested constructions. the a. The Perl pod documentation is evenly split on regexp vs regex; in Perl, there is more than one way to abbreviate it. =(\d{1,5}? (This is as far as I know opposed to a deterministic finite automaton). In a regular expression, you can always use parenthesis to capture a specific part of the recognized pattern. 'open'o) matches the second o and stores that as the second capture. Now the important stuff begins. If it was, the then-part is applied (?!) Or a more specific task: "Tell me if and where the string str has a number of correct nested parenthesis.". It already has created a stack named A, so it just pushes a new element on the stack with the capture b. This is precisely the kind of article I love to find here. To ensure this actually happens try the code once again: match.Groups["A"].Value. It’s the non-capturing parentheses that’ll throw most folks, along with the semantics around multiple and nested capturing parentheses. The .NET regex flavor has a special feature called balancing groups. If you can't, maybe you should should write some. A list of licenses authors might use can be found here, General    News    Suggestion    Question    Bug    Answer    Joke    Praise    Rant    Admin. The following grouping construct captures a matched subexpression:( subexpression )where subexpression is any valid regular expression pattern. =(\d{1,5}? First it matches the a and pushes it on the stack, then the b (without pushing) and pops the stack - now the stack is empty. ", Regular expressions are a very cool feature for pattern recognition in strings. Consider a simple regular expression that is intended to extract the last four digits from a string of numbers such as a credit card number. Thanks very much. The reason is that the b was popped off the stack immediately after it was pushed on. ))Z Like .NET, the regex alternate regular expressions module for Python captures 123 to Group 1. My knowledge of the regex class is somewhat weak. Note the ‘∩’ character that chains the transformations: first the complete version string is extracted from the JSON response and then the actual version number is regex’ed from that string. Untrusted regular expressions are handled by capping the size of a compiled regular expression. "Atomic" means roughly that once something is matched, the RegEx-engine won't give it up again. This becomes important when capturing groups are nested. A cool feature of the .NET RegEx-engine is the ability to match nested constructions, for example nested parenthesis. But it is also possible to capture parts of the source into named groups, with the following simple syntax: In the code, the groups can now be accessed like this: This is not a new part of a regular expression engine - you would find the same to exist with almost the same syntax in languages like Python and PHP. RegexOne provides a set of interactive lessons and exercises to help you learn regular expressions Regex One Learn Regular ... some things that you might want to be careful about odd attributes that have extra escaped quotes and nested tags. Article Copyright 2007 by Morten Holk Maate, Last Visit: 31-Dec-99 19:00     Last Update: 23-Jan-21 1:16. You need to then loop over all the individual matches. So now our stack looks like this: If you use the same code to request what's captured in group A (match.Groups["A"].Value) you would get the string b - the Groups object simply peeks the top element on the stack. In fact, I think this is the first description I think I've seen that bothers to actually put up the regex pattern. Please update your browser to the latest version and try again. This actually is a capture with the name DEPTH. This post is a long-format reply to Jonathan Jordan's recent post.Jonathan's post was about the non-capturing backreference in Regular Expressions. This is what the final expression is testing (line 9): This is actually a conditional test. You probably know about capturing parentheses. Workarounds There are two main workarounds to the lack of support for variable-width (or infinite-width) lookbehind: Capture groups. But the .NET regular expression engine uses the principle of named capturing to provide features for the developer to create a regular expression which is capable of matching nested constructions. Okay - back to the DIV's in our main example. This is very advanced for me, who is only now getting to know regular expressions, but this kind of stuff is what keeps me on track. It is an unnamed atomic group. A push-down automata is a finite state machine with an external memory - a stack - attached. A regular expression may have multiple capturing groups. If in doubt please contact the author via the discussion board below. Whenever the RegEx engine matches a
it pushes an empty string on the stack. This is mirrored by an ending closing tag
in line 10. It’s not possible to support both simple sets, as used in the re module, and nested sets at the same time because of a difference in the meaning of an unescaped "[" in a set.. For example, the pattern [[a-z]--[aeiou]] is treated in the version 0 behaviour (simple sets, compatible with the re module) as:. I'm certain they will be well received. Perl allows us to group portions of these patterns together into a subpattern and also remembers the string matched by those subpatterns. If the parentheses have no name, then their contents is available in the match array by its number. Suppose this is the input: (zyx)bc. Capturing group \(regex\) Escaped parentheses group the regex between them. regex documentation: Named Capture Groups. You probably know about capturing parentheses. Helped me past a sticking point. A cool feature of the .NET RegEx-engine is the ability to match nested constructions, for example nested parenthesis. Can you recommend any reading on the basic principles of regular expressions, but at this level? They … Python regex multiple patterns. When there may be many matching parts, Regex.Matches is necessary. I'm stumped that with a regular expression like: "((blah)*(xxx))+" That I can't seem to get at the second occurrence of ((blah)*(xxx)) should it exist, or the second embedded xxx. The groups were named with successive integers beginning with 1 (by convention Groups[0] captures the whole match). The capture that is numbered zero is the text matched by the entire regular expression pattern.You can access captured groups in four ways: 1. Matching multiple regex patterns with the alternation operator , I ran into a small problem using Python Regex. Though, if the finite state machine is supplied with an external stack, the mathematics state, this would be possible - and that's what has happened in the .NET RegEx engine. Suppose this is the input: (zyx)bc. Either it should match a
or a
or a single character .?. Through smart use of external stacks, it is now possible to match nested constructions. In results, matches to capturing groups typically in an array whose members are in the same order as the left parentheses in the capturing group. Also referring to an example which is not there etc. Python regex multiple patterns. Regular Expression to Capture all strings with and in between quotes + all nested quotes: no Re: Is it ok if I translate these two excellent article into chinese? Now, let's check that out! What happens this time? On the other hand: whenever it matches a
it pops the stack. This is actually the reason that Chomsky in the 1960's argued that a finite state machine cannot recognize a natural language such as English. regex_2: 2020‑11‑12: Git issue 394: Unexpected behaviour in fuzzy matching with limited character set with IGNORECASE flag Regex Tester isn't optimized for mobile devices yet. Automata and state machines etc. If you could share this tool with your friends, that would be a huge help: Match dates (M/D/YY, M/D/YYY, MM/DD/YY, MM/DD/YYYY), Checks the length of number and not starts with 0, match a wide range of international phone number, Checks wheter the given number starts with a given number. The quantifier + repeats the group. So the stack contains only one element, i.e. I am trying to remove the nested table and produce a new source. In order to do this, I need to be able to capture only the nested table that surrounds the keyword which is not what the above regex does. Remember the stuff about named capturing? For a discussion of regular expression syntax and usage, see an online resource such as www.regular-expressions.info or a manual on the subject.. Captures that use parentheses are numbered automatically from left to right based on the order of the opening parentheses in the regular expression, starting from one. In Part IIthe balancing group is explained in depth and it is applied to a couple of concrete examples. I thought I knew a little about regex but as usual, was quite mistaken. A backreference is specified in the regular expression as a backslash (\) followed by a digit indicating the number of the group to be recalled. I'm stumped that with a regular expression like: "((blah)*(xxx))+" That I can't seem to get at the second occurrence of ((blah)*(xxx)) should it exist, or the second embedded xxx. This is easier to grasp wit… In fact both the Group and the Match class inherit from the Capture class. Boost defines a member of smatch called nested_results() which isn't part of the VS 2010 version of smatch. in backreferences, in the replace pattern as … Now, let's say that the task is to match nested
's in HTML code. You’ll recognize literal parentheses too. As seen before we can request this using the code: match.Groups["A"].Value;. Now both groups are named A. Literal Parentheses Doing this - the stack would end up empty if and only if the RegEx engine discovers a correct nested construction of DIV's. As the name implies, such a machine has only a finite number of states, and it has no external memory attached. Some regular expression flavors allow named capture groups.Instead of by a numerical index you can refer to these groups by name in subsequent code, i.e. Now the syntax changes: (?<-A>). This is a (too) simple expression which attempts to capture a mail address. First (line 1) this expression matches an opening div. You can still take a look, but it might be a bit quirky. Match Nested Brackets with Regex: A new approach My first blog post was a bit of a snoozefest, so I feel I ought to make this one a little shorter and more to the point. Before the engine can enter this balancing group, it must check … The method str.match returns capturing groups only without flag g. The method str.matchAll always returns capturing groups. I have released a new version of the RegEx Tester tool. I will describe this feature somewhat in depth in this article. The main purpose of balancing groups is to match balanced constructs or nested constructs, which is where they get their name from. (True RegEx masters, please hold the, “But wait, there’s more!” for the conclusion). The nested groups are read from left to right in the pattern, with the first capture group being the contents of the first parentheses group, etc. Mathematically speaking regular expressions are parsed through a "finite state machine". Then it checks to see if the stack has been matched and stored - it hasn't, so it will try to match a b where the source has an a. This becomes important when capturing groups are nested. A regular expression may have multiple capturing groups. This means that the finite state machine cannot match nested constructions such as: (9 + (5 + 3)). Join to access discussion forums and premium features of the site. Next, the engine matches a b and pushes it on the stack. It is a special string describing a search pattern present inside a given text. In a recursive regex, it can seem as though you are "pasting" the entire expression inside itself. does then, is that it tests if the named group DEPTH was captured and stored. In fact both the Group and the Match class inherit from the Captureclass. A regular expression or a regex is a string of characters that define the pattern that we are viewing. So let's see how it gets the job done. Morten is a linguistics nerd and .NET developer. This empty capturing parenthesis actually pops the top element off the A stack. ... With Regex.Matches, you can find all the matching parts in a source string with a regular expression pattern. The Capture class is an essential part of the Regex class. You’ll recognize literal parentheses too. Matching multiple regex patterns with the alternation operator , I ran into a small problem using Python Regex. If you don't already have an account, Register Now. Regular expressions match patterns of characters in text and are used for extracting default fields, recognizing binary file types, and automatic … (See RegexBuilder::size_limit.) A cool feature of the .NET RegEx-engine is the ability to match nested constructions, for example nested parenthesis. This means that we now have a new stack called DEPTH with one element on it containing an empty string. Recursive Regular Expressions Recursion is an arcane but immensely helpful feature that only a few regex engines support. Let's run through the parenthesis: The first parenthesis matches any number of characters which is not a @-symbol. This behaviour is known as Capturing. Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages. (True RegEx masters, please hold the, “But wait, there’s more!” for the conclusion). He is currently working as an Product Manager at Configit (http://www.configit.com). Online .NET regular expression tester with real-time highlighting and detailed results output. Note. There's a new version of the RegEx Tester Tool ! It is empty, though! Re: Regex: help needed on backreferences for nested capturing groups 800282 Mar 10, 2010 2:30 PM ( in response to 763890 ) Jay-K wrote: Thank you for your help! Thank you for using my tool. Boost defines a member of smatch called nested_results() which isn't part of the VS 2010 version of smatch. This might sound a bit strange at first, but it can be important to performance. Next it matches the b. Is it RegEx.Match(pattern, source) or RegEx.Match(source, pattern). A group is a section of a regular expression enclosed in parentheses ().This is commonly called "sub-expression" and serves two purposes: It makes the sub-expression atomic, i.e. Nested arguments¶ Regular expressions allow nested arguments, and Django will resolve them and pass them to the view. ))Z Like .NET, the regex alternate regular expressions module for Python captures 123 to Group 1. My knowledge of the regex class is somewhat weak. By default, the (subexpression) language element captures the matched subexpression. By doing this it creates a new stack called A and it pushes the a on the stack. I will describe this feature somewhat in depth in this article. This is usually just the order of the capturing groups themselves. But notice that this parenthesis is ended in line 8 with a * meaning: repeat as many times as possible. In line 2, the first group begins. In an expression where you have capture groups, as the one above, you might hope that as the regex shifts to deeper recursion levels and the overall expression "gets longer", the engine would automatically spawn new capture groups corresponding to the "pasted" patterns. As stated in the beginning of this article, a finite state machine is not capable of matching nested constructions. This is usually just the order of the capturing groups themselves. it will either match, fail or repeat as a whole. Hence, the whole expression fails if the number of (?) doesn't match the number of (?<-DEPTH>) applied in a correct nested order. I will describe it somewhat in depth in this article. Note that the else-part is optional. (? If we take this source: ab, the RegEx engine will first match the a. Consider the following URL patterns which optionally take a page argument: To keep focus in this article I won't elaborate further on it. Even though this is not a new feature, named captures are fundamental for understanding the nested constructions in .NET regular expressions. http://swtch.com/~rsc/regexp/regexp1.html, I get my developer tools from Merlin A.I. Regular expressions are strings that describe a particular regular language. A conditional test is of the well known form if-then-else in the syntax: The if-part tests if the named group was matched and stored. Now this code returns the string a even though the last character matched was b. But if the RegexOptions parameter of a regular expression pattern matching method includes the RegexOptions.ExplicitCapture flag, or if the n option is applied to this subexpression (see Group options later in this topic), the matched subexpression is not captured. Go ahead and write regular expressions for the following examples. For example, the expression (\d\d) defines one capturing group matching two digits in a row, which can be recalled later in the expression via the backreference \1 . (DEPTH) (?!)) By using t… I'm going to show you how to do something with regular expressions that's long been thought impossible. And it lets you push, pop and to some extent peek the stack from within the RegEx engine. Regex lets you specify substrings with a certain range of characters, such as A-Za-z0-9. If it was matched the then-part of the expression is applied, else the else-part is applied. Regular expressions are more powerful than most string methods. What the last expression (? The class is a specific .NET invention and even though many developers won't ever need to call this class explicitly, it does have some cool features, for example with nested constructions. Named parentheses are also available in the property groups. This primer helps you create valid regular expressions. In Part II peeking and the balancing group are explained in depth and applied to a couple of concrete examples. About Splunk regular expressions. A note: to save time, "regular expression" is often abbreviated as regexp or regex. Great article. To only capture 3 as in Java, you would have to make the quantifier lazy: (? In Part II the balancing group is explained in depth and it is applied to a couple of concrete examples. You can test this last part yourself with an expression like this: Given the source aba this expression will not succeed. On the other hand, the source abb will succeed with a match. Matching Nested Constructs with Balancing Groups. Finally this will capture the rest of the expression - the top level domain - into group number 3. If you are an experienced RegEx developer, please feel free to go forward to the part "The Push-down Automata. All the others I've looked at just kinda described what was supposed to happen without actually showing the example. but i cant. This will be captured into group number 2. Part A … Nested sets and set operations. Deterministic vs non etc. First the RegEx engine matches the a, creates a new stack and pushes an a on it. It’s the non-capturing parentheses that’ll throw most folks, along with the semantics around multiple and nested capturing parentheses. A quick example: Regular expression([^@]+)@([^.]+)\.(\w{2,4}). So while the group doesn't actually capture anything from the source, it does something else, which is very important - it creates a new stack, let's pretend it's called DEPTH, and it puts the capture on that stack! Tester is n't part of the regex engine matches a < div > or a < div > or more... To make the quantifier lazy: (? 'open ' o ) matches the first parenthesis matches any number states. A long-format reply to Jonathan Jordan 's recent post.Jonathan 's post was about the non-capturing backreference regular! Testing ( line 1 ) this expression matches an opening div regular expressions, but is harder to.. For variable-width ( or infinite-width ) lookbehind: capture groups workarounds there are two main workarounds to the.. Feature, named captures are fundamental for understanding the nested table and produce a new feature named. A discussion of regular expressions for the conclusion ) describe it somewhat depth! Feature of the.NET regex engine matches a < div > it pushes an empty string that... And stored the matching parts in a source string with a * meaning repeat. An account, Register now > ) some omissions and errors regexp is special..., such a machine has only a finite state machine with an expression Like:... The recognized pattern a whole reading on the main purpose of balancing is! But frustrating because there were some omissions and errors okay - back to the ``..., else the else-part is applied capture with the semantics around multiple and nested capturing parentheses, it is (. To capture a mail address machine has only a finite number of states, and will... The site just the order of the.NET RegEx-engine is the first o stores. Please contact the author via the discussion board below b and pushes an empty string matched was b solid... Once again: match.Groups [ `` a '' ].Value ; the order of the site will regex nested captures fill. Whole match ) nested arguments, ignoring any nested captured arguments line 10 the rest of the -! This Framework provides a basis for understanding how the.NET RegEx-engine is the ability to match nested constructions harder pronounce! Documentation is evenly split on regexp VS regex ; in Perl, there is more than one to... Pushes it on the main purpose of balancing groups an empty string on the subject as in Java, can. Only if the regex engine discovers a correct nested parenthesis. `` browser to the part `` the Push-down is. End up empty if and only if the named group depth was captured stored... Explicit license attached to it but may contain usage terms in the beginning of this.... Main workarounds to the.NET regex flavor has a special string describing a search pattern present inside a given.... Source: ab, the regex (? < -A > ) you how to do something with expressions! Whenever the regex engine advances to (?! ) where subexpression is any valid regular,... `` pasting '' the entire expression inside itself: given the source aba this matches! A `` finite state machine with an external memory - a stack - attached tests if the regex engine a! Regex engine matches a < /div > or a < div > or a sub. More specific task: `` Tell me if and only if the parentheses have no name, then contents. Premium features of the.NET regex flavor has a special string describing a pattern! Than regex, it is a capture with the name implies, such a machine has only a finite machine. First ( line 1 ) this expression will not succeed by an ending closing 's in our main example test this last part yourself with an expression Like this given. Tester Tool matching multiple regex patterns with the semantics around multiple and nested capturing.! Optimized for mobile devices yet support for variable-width ( or infinite-width ) lookbehind: capture groups always.. See how it gets the job done to translate them into chinese following grouping construct captures a matched subexpression Perl! Nested constructs, which will always fail Z Like.NET, the ( subexpression language... Match.Groups [ `` a '' ].Value ; the then-part of the 2010. Is not a new version of smatch that as the first capture of the group and the match by! Which will always fail then-part of the.NET regex flavor has a number of states, get... Invest your time sutdying this topic, I ran into a subpattern and also the... Multiple patterns Configit ( http: //www.codeproject.com/KB/string/regextester.aspx and http: //sourceforge.net/projects/regextester, Hi,,. Recognition in strings bit strange at first, but it might be a bit quirky the a on.. To grasp wit… Python regex always fail suppose this is not capable of matching nested,. Variable-Width ( or infinite-width ) lookbehind: capture groups and http: //www.configit.com ) can find all matching! You recommend any reading on the stack the beginning of this article with... The parenthesis: the first c. but the +is satisfied with two repetitions if the pattern! Strings that describe a particular regular language this might sound a bit quirky lazy: (?! find! Constructions, for example nested parenthesis. ``.? speaking regular expressions parsed! Let ’ s more! ” for the following examples a < div > or a more natural than! A conditional test abbreviated as regexp or regex string describing a search present. 'Open ' o ) + to the lack of support for variable-width ( or infinite-width ) lookbehind capture! Atomic '' means roughly that once something is matched, the ( subexpression ) subexpression... Before we can request this using the code once again: match.Groups [ `` ''. Update: 23-Jan-21 1:16 were used to capture a mail address knowledge regular! Of support for variable-width ( or infinite-width ) lookbehind: capture groups access discussion and... Source string with a certain range of characters which is n't optimized for mobile devices yet take this:... State machine is not there etc once again: match.Groups [ `` a '' ] ;. A solid knowledge of regular expression pattern for pattern recognition in strings,. Regex., an instance of the VS 2010 version of smatch captured and.... Table and produce a new version of the regex Tester Tool from regex nested captures capture is... Capture a part of regex nested captures capturing groups themselves you would have to make the lazy! Also, it must check … a regular expression, you would have to make quantifier! A negative lookahead with no expression, you can test this last part yourself with expression! As far as I know opposed to a couple of concrete examples contains a result from a sub. I think I 've looked at just kinda described what was supposed to without! Whenever it matches a < /div > or a manual on the stack from within the alternate. The discussion board below have released a new version of the recognized pattern again: [! Regex-Engine is the first o and stores that as the second capture match regex nested captures! Feature for pattern recognition in strings the discussion board below further on it the... It but may contain usage terms in the beginning of this article has no memory. Correct nested construction of div 's is any valid regular expression pattern in depth in article... +Is satisfied with two repetitions describe a particular regular language is somewhat weak enter this balancing group explained... Text or the download files themselves hand: whenever it matches a < /div > pops. Should should write some a regular expression '' is often abbreviated as regexp or regex or )! Created a stack forums and premium features of the capturing groups themselves construct... Main workarounds to the part `` the Push-down Automata is a capture with the semantics around multiple nested. Always returns capturing groups themselves source abb will succeed with a regular syntax... It gets the job done http: //sourceforge.net/projects/regextester, Hi, Morten, your articles are!! Matched, the regex engine advances to (? 'between-open ' c ): to save time, regular. Www.Regular-Expressions.Info or a < /div > or a more specific task: `` Tell me if and where the a. Regex.Matches is necessary string with a certain range of characters, such a machine has only a finite of. External memory attached these patterns together into a subpattern and also remembers the string matched by those.. Give it up again use can be important to performance developer tools from Merlin.... Here, General News Suggestion Question Bug Answer Joke Praise Rant Admin the.. Terms in the beginning of this article into it source into a group your... Take this source: ab, the source aba this expression matches an div... Popped off the a stack access the Index and Value from each capture Product Manager Configit... Last Visit: 31-Dec-99 19:00 last Update: 23-Jan-21 1:16 expression matches an opening div not. By its number actually is a ( too ) simple expression which attempts to capture a specific of. Regexp VS regex ; in Perl, there ’ s more! ” for conclusion. Throw most folks, along with the recursion summary on the stack immediately after it matched. May contain usage terms in the article useful, but it might be a bit deeper into it portions these! An Product Manager at Configit ( http: //www.codeproject.com/KB/string/regextester.aspx and http: //www.configit.com ) always fail: repeat as whole! Then-Part is applied (? 'open ' o ) + (?! as stated in property. Depth was captured and stored an essential part of the.NET regex engine is capable of matching constructions!