One also could look at it the other way around: an URL always matches any string, that includes Javascript code. Here is a nice example from the real world: Wh

One also could look at it the other way around: an URL always matches any string, that includes Javascript code. Here is a nice example from the real world: Whenever I use the Regex engine of XML Schema (or later XPath), with the regular expression shown in RFC3986 - Uniform Resource Identifier (URI): Generic Syntax, I get the error: "Regular expression matches any string.". (The reason for this being an error is, that the XSD regex engine had only one purpose: to constrain a string, so we can check for valid input or define a datatype. That's why it behaves that way.) Here is the part with the regex from Appendix B[1] of aforementioned RFC: The following line is the regular expression for breaking-down a well-formed URI reference into its components. ^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(\?([^#]*))?(#(.*))? 12 3 4 5 6 7 8 9 The numbers in the second line above are only to assist readability; they indicate the reference points for each subexpression (i.e., each paired parenthesis). We refer to the value matched for subexpression <n> as $<n>. For example, matching the above expression to http://www.ics.uci.edu/pub/ietf/uri/#Related results in the following subexpression matches: $1 = http: $2 = http $3 = //www.ics.uci.edu $4 = www.ics.uci.edu $5 = /pub/ietf/uri/ $6 = <undefined> $7 = <undefined> $8 = #Related $9 = Related where <undefined> indicates that the component is not present, as is the case for the query component in the above example. Therefore, we can determine the value of the five components as scheme = $2 authority = $4 path = $5 query = $7 fragment = $9 [1]: https://datatracker.ietf.org/doc/html/rfc3986#appendix-B https://datatracker.ietf.org/doc/html/rfc3986#appendix-B