This one gets close to handling most valid email address examples using the specification from RFC 282 ISO standard __ It doesn'T handle everything but manages fairly well...

X3D Regular Expressions (regexes): MFBool X3D MFBool is a list of boolean values, separated by whitespace or comma values http://www.web3d.org/specifications/X3dRegularExpressions.html#MFBool

X3D SFBool X3D SFBool is a single-field boolean value. http://www.web3d.org/specifications/X3dRegularExpressions.html#SFBool

X3D SFBool X3D SFBool is a single-field boolean value. http://www.web3d.org/specifications/X3dRegularExpressions.html#SFBool

Extensions sourced from here#Suffixes_for_compressed_files),

preg_replace( '', '%newline%', $string )

devtable.config id="CodPay"

Handles single letter usernames, initial / trailing / consecutive periods, max length of 30 letters.

Parse the Accept request HTTP header advertises which content types, expressed as MIME types, https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Accept

Primer ejercicio del Curso de Expresiones Regulares

Curso de Expresiones Regulares: Modos

Curso de Expresiones Regulares: Meta Caracteres

Curso de Expresiones Regulares: Cuantificadores y Repetición