In what contexts can I use the greater than symbol < as text in HTML?
For example < & <= parse render as text perfectly fine if they are in a tag:
<p>
<
<=
</p>
However <t will be parsed as HTML by the browser and not produce the text <t.
Is there a rule for what characters can proceed the greater than symbol for the browser to assume that it is the start of a tag?
The rule is: almost never.
Only inside quoted attribute values (and in raw text tags like script and style) are you permitted to write < unescaped. I think attribute names permit these too, but not > (though why you would put a < in an attribute name is beyond me).
Browsers will do their best to recover from bad HTML, so sometimes you might get away with it if you forget.
But it's best to always encode your entities.
You should scan the HTML spec, but here's one relevant chapter with some of the constraints listed in various sections.
Use an HTML validator in strict mode to make sure you're getting it right; the HTML you gave in your question is rejected by the linked tool, with a suggestion to switch to <.
My problem occurs when I try to use some data/strings in a p-element.
I start of with data like this:
data: function() {
return {
reportText: {
text1: "This is some subject text",
text2: "This is the conclusion",
}
}
}
I use this data as follows in my (vue-)html:
<p> {{ reportText.text1 }} </p>
<p> {{ reportText.text2 }} </p>
In my browser, when I inspect my elements I get to see the following results:
<p>This is some subject text</p>
<p>This is the conclusion</p>
As you can see, there is suddenly a difference, one p element uses and the other , even though I started of with both strings only using . I know and technically represent the same thingm, but the problem with the string is that it gets treated as a string with 1 large word instead of multiple separate words. This screws up my layout and I can't solve this by using certain css properties (word-wrap etc.)
Other things I have tried:
Tried sanitizing the strings by using .replace( , ), but that doesn't do anything. I assume this is because it basically is the same, so there is nothing to really replace. Same reason why I have to use blockcode on stackoverflow to make the destinction between and .
Logged the data from vue to see if there is any noticeable difference, but I can't see any. If I log the data/reportText I again only see string with 's
So I have the following questions:
Why does this happen? I can't seem to find any logical explanation why it sometimes uses 's and sometimes uses 's, it seems random, but I am sure I am missing something.
Any other things I could try to follow the path my string takes, so I can see where the transformation from to happens?
Per the comments, the solution devised ended up being a simple unicode character replacement targeting the \u00A0 unicode code point (i.e. replacing unicode non-breaking spaces with ordinary spaces):
str.replace(/[\\u00A0]/g, ' ')
Explanation:
JavaScript typically allows the use of unicode characters in two ways: you can input the rendered character directly, or you can use a unicode code point (i.e. in the case of JavaScript, a hexadecimal code prefixed with \u like \u00A0). It has no concept of an HTML entity (i.e. a character sequence between a & and ; like ).
The inspector tool for some browsers, however, utilizes the HTML concept of the HTML entity and will often display unicode characters using their corresponding HTML entities where applicable. If you check the same source code in Chrome's inspector vs. Firefox's inspector (as of writing this answer, anyway), you will see that Chrome uses HTML entities while Firefox uses the rendered character result. While it's a handy feature to be able to see non-printable unicode characters in the inspector, Chrome's use of HTML entities is only a convenience feature, not a reflection of the actual contents of your source code.
With that in mind, we can infer that your source code contains unicode characters in their fully rendered form. Regardless of the form of your unicode character, the fix is identical: you need to target these unicode space characters explicitly and replace them with ordinary spaces.
Is there a tool that compares an HTML document like:
<p b="1" a="0 "> a b
c </p>
(as a C string: "<p> a b\nc </p>") equal to:
<p a="0 " b="1">a b c</p>
Note how:
text multiple whitespaces were converted to a single whitespace
newlines were converted to whitespaces
text trailing and heading whitespaces were stripped
attributes were put on a standard order
attribute values were unchanged, including trailing whitespaces
Why I want that
I am working on the Markdown Test Suite that aims to measure markdown engine compliance and portability.
We have markdown input, expected HTML output, and want to determine if the generated HTML output is equal to the expected one.
The problem is that Markdown is underspecified, so we cannot compare directly the two HTML strings.
The actual test code is here, just modify run-tests.py#dom_normalize if you want to try out your solution.
Things I tried
beautifulsoup. Orders the attributes, but does not deal well with whitespaces?
A function formatter regex modification might work, but I don't see a way to differentiate between the inside of nodes and attributes.
A Python only solution like this would be ideal.
looking for a Javascript function similar to isEqualNode() (does not work because ignores nodeVaue) + some headless JS engine. Couldn't find one.
If there is nothing better, I'll just have to write my own output formatter front-end to some HTML parser.
I ended up cooking up a custom HTML renderer that normalizes things based on Python's stdlib HTMLParser.
You can see it at: https://github.com/karlcow/markdown-testsuite/blob/749ed0b812ffcb8b6cc56f93ff94c6fdfb6bd4a2/run-tests.py#L20
Usage and docstrig tests at: https://github.com/karlcow/markdown-testsuite/blob/749ed0b812ffcb8b6cc56f93ff94c6fdfb6bd4a2/run-tests.py#L74
I need to parse a html document that has been generated by saving a word document as html.
I have been using the HTML agility pack quite successfully but in this instance I figured using regex for this one part might be easier (opinions?)
Word generates the following code when it translates one of its footnotes into html
<a href="#_ftn2" name="_ftnref2" title=""><span
class=MsoFootnoteReference><span class=MsoFootnoteReference><span
style='font-size:10.0pt'>[2]</span></span></span></a>
This output is consistent for every footnote with only the href= and name changing as well as the [2] text.
I need to extract the _ftn2 and [2] elements.
So far I have the following regex which will extract the _ftn2 part into the name group
<a href="#(?<name>_ftn\d).*>(<span class=MsoFootNoteReference>)
I'm having a bit of trouble parsing the second bit with all those span tags.
Is it going to be easier to use regex for this or should I continue to use the HAP for this part?
An an aside does anyone know why word generates nested identical span tags
<span class=MsoFootnoteReference>
If the input follows exactly that format then you can get away with a pretty loose regex. You just need to ignore everything except the parts you want to extract and then employ non-greedy expressions to eat up all the garbage between them:
<a href="#(?<name>_ftn\d).*?(?<number>\[\d+\]).*?<\/a>
You can use a non-greedy .*? to eat up all the extra markup because nothing in there will match your next \[\d+\] pattern. You don't really need the .*?<\/a> bit on the end, that's mostly for symmetry and a bit of extra paranoia.
Something like this is probably one of the few cases where using regular expressions to rip apart HTML makes sense. You could do this sort of thing with an HTML parser but then you'd be a nightmare of twisty XPath expressions (all of which look alike), DOM manipulations, or SAX events. And you might even get eaten by a grue.
I am creating an application that will take a URL as input, retrieve the page's html content off the web and extract everything that isn't contained in a tag. In other words, the textual content of the page, as seen by the visitor to that page. That includes 'masking' out everything encapsuled in <script></script>, <style></style> and <!-- -->, since these portions contain text that is not enveloped within a tag (but is best left alone).
I have constructed this regex:
(?:<(?P<tag>script|style)[\s\S]*?</(?P=tag)>)|(?:<!--[\s\S]*?-->)|(?:<[\s\S]*?>)
It correctly selects all the content that i want to ignore, and only leaves the page's text contents. However, that means that what I want to extract won't show up in the match collection (I am using VB.Net in Visual Studio 2010).
Is there a way to "invert" the matching of a whole document like this, so that I'd get matches on all the text strings that are left out by the matching in the above regex?
So far, what I did was to add another alternative at the end, that selects "any sequence that doesn't contain < or >", which then means the leftover text. I named that last bit in a capture group, and when I iterate over the matches, I check for the presence of text in the "text" group. This works, but I was wondering if it was possible to do it all through regex and just end up with matches on the plain text.
This is supposed to work generically, without knowing any specific tags in the html. It's supposed to extract all text. Additionally, I need to preserve the original html so the page retains all its links and scripts - i only need to be able to extract the text so that I can perform searches and replacements within it, without fear of "renaming" any tags, attributes or script variables etc (so I can't just do a "replace with nothing" on all the matches I get, because even though I am then left with what I need, it's a hassle to reinsert that back into the correct places of the fully functional document).
I want to know if this is at all possible using regex (and I know about HTML Agility Pack and XPath, but don't feel like).
Any suggestions?
Update:
Here is the (regex-based) solution I ended up with: http://www.martinwardener.com/regex/, implemented in a demo web application that will show both the active regex strings along with a test engine which lets you run the parsing on any online html page, giving you parse times and extracted results (for link, url and text portions individually - as well as views where all the regex matches are highlighted in place in the complete HTML document).
what I did was to add another alternative at the end, that selects "any sequence that doesn't contain < or >", which then means the leftover text. I named that last bit in a capture group, and when I iterate over the matches, I check for the presence of text in the "text" group.
That's what one would normally do. Or even simpler, replace every match of the markup pattern with and empty string and what you've got left is the stuff you're looking for.
It kind of works, but there seems to be a string here and there that gets picked up that shouldn't be.
Well yeah, that's because your expression—and regex in general—is inadequate to parse even valid HTML, let alone the horrors that are out there on the real web. First tip to look at, if you really want to chase this futile approach: attribute values (as well as text content in general) may contain an unescaped > character.
I would like to once again suggest the benefits of HTML Agility Pack.
ETA: since you seem to want it, here's some examples of markup that looks like it'll trip up your expression.
<a href=link></a> - unquoted
<a href= link></a> - unquoted, space at front matched but then required at back
- very common URL char missing in group
- more URL chars missing in group
<a href=lïnk></a> - IRI
<a href
="link"> - newline (or tab)
<div style="background-image: url(link);"> - unquoted
<div style="background-image: url( 'link' );"> - spaced
<div style="background-image: url('link');"> - html escape
<div style="background-image: ur\l('link');"> - css escape
<div style="background-image: url('link\')link');"> - css escape
<div style="background-image: url(\
'link')"> - CSS folding
<div style="background-image: url
('link')"> - newline (or tab)
and that's just completely valid markup that won't match the right link, not any of the possible invalid markup, markup that shouldn't but does match a link, or any of the many problems with your other technique of splitting markup from text. This is the tip of the iceberg.
Regex is not reliable for retrieving textual contents of HTML documents. Regex cannot handle nested tags. Supposing a document doesn't contain any nested tag, regex still requires every tags are properly closed.
If you are using PHP, for simplicity, I strongly recommend you to use DOM (Document Object Model) to parse/extract HTML documents. DOM library usually exists in every programming language.
If you're looking to extract parts of a string not matched by a regex, you could simply replace the parts that are matched with an empty string for the same effect.
Note that the only reason this might work is because the tags you're interested in removing, <script> and <style> tags, cannot be nested.
However, it's not uncommon for one <script> tag to contain code to programmatically append another <script> tag, in which case your regex will fail. It will also fail in the case where any tag isn't properly closed.
You cannot parse HTML with regular expressions.
Parsing HTML with regular expressions leads to sadness.
I know you're just doing it for fun, but there are so many packages out there than actually do the parsing the right way, AND do it reliably, AND have been tested.
Don't go reinventing the wheel, and doing it a way that is all but guaranteed to frustrate you down the road.
OK, so here's how I'm doing it:
Using my original regex (with the added search pattern for the plain text, which happens to be any text that's left over after the tag searches are done):
(?:(?:<(?P<tag>script|style)[\s\S]*?</(?P=tag)>)|(?:<!--[\s\S]*?-->)|(?:<[\s\S]*?>))|(?P<text>[^<>]*)
Then in VB.Net:
Dim regexText As New Regex("(?:(?:<(?<tag>script|style)[\s\S]*?</\k<tag>>)|(?:<!--[\s\S]*?-->)|(?:<[\s\S]*?>))|(?<text>[^<>]*)", RegexOptions.IgnoreCase)
Dim source As String = File.ReadAllText("html.txt")
Dim evaluator As New MatchEvaluator(AddressOf MatchEvalFunction)
Dim newHtml As String = regexText.Replace(source, evaluator)
The actual replacing of text happens here:
Private Function MatchEvalFunction(ByVal match As Match) As String
Dim plainText As String = match.Groups("text").Value
If plainText IsNot Nothing AndAlso plainText <> "" Then
MatchEvalFunction = match.Value.Replace(plainText, plainText.Replace("Original word", "Replacement word"))
Else
MatchEvalFunction = match.Value
End If
End Function
Voila. newHtml now contains an exact copy of the original, except every occurrence of "Original word" in the page (as it's presented in a browser) is switched with "Replacement word", and all html and script code is preserved untouched. Of course, one could / would put in a more elaborate replacement routine, but this shows the basic principle. This is 12 lines of code, including function declaration and loading of html code etc. I'd be very interested in seeing a parallel solution, done in DOM etc for comparison (yes, I know this approach can be thrown off balance by certain occurrences of some nested tags quirks - in SCRIPT rewriting - but the damage from that will still be very limited, if any (see some of the comments above), and in general this will do the job pretty darn well).
For Your Information,
Instead of Regex, With JQuery , Its possible to extract text alone from a html markup. For that you can use the following pattern.
$("<div/>").html("#elementId").text()
You can refer this JSFIDDLE