Errata

page 11: Anchors and zero-width assertions (all languages mentioned in book)

"When supported, \Z matches the end of string or before
a string-ending newline, regardless of match mode."
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pg 46, table 1-23 (Python)

Sequence : Meaning
\Z : End of string or before a string-ending newline, in any match mode

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The following program, run by python 3.65, shows that \Z (unlike $)
does not match "before a string-ending newline"

import re

if re.search(r'foo$', 'foo\n'): print("foo\\n matched with $")
if re.search(r'foo\Z', 'foo\n'): print("foo\\n matched with \Z")

The dot will match newline IF the m modifier is used, not the s modifier. In Ruby, it is by default multiline as in other language -- that is, the ^ and $ will match the newline characters in Ruby by default.

In most other languages, the s modifier makes the dot match a newline character. In Ruby, it is the m modifier.

\W Nonword character, the Unicode property is the positive \p{Xx) not the negative \P{Xx}

I would like to mention the below printing mistakes on page 23 (Table 9).

$' - It should return 'Text after match' (' single quote)
$` - It should return 'Text before match' (` back tick)

\t is not a vertical tab..\v is