Name a scripting language that uses dynamic scoping. Summarize the strategies used in Perl, PHP, Ruby, and Python to determine the scope of variables that are not declared. Describe the conceptual...

Name a scripting language that uses dynamic scoping. Summarize the strategies used in Perl, PHP, Ruby, and Python to determine the scope of variables that are not declared. Describe the conceptual model for dynamically scoped variables in Perl. List the principal features found in POSIX regular expressions, but not in the regular expressions of formal language theory (Section 2.1.1).