In PHP, when you use heredoc syntax to define a string, do variables inside the heredoc content get parsed and substituted, and how does this compare to single quoted and double quoted strings?

Introduction / Context:
PHP supports several ways to declare string literals, including single quoted strings, double quoted strings, heredoc, and nowdoc. Each has different rules for how variables and escape sequences are handled. This question focuses on heredoc syntax and whether PHP performs variable substitution inside a heredoc block, which is an important detail for writing readable templates and multi line messages.

Given Data / Assumptions:

• The language is PHP.
• The syntax in question is heredoc, which uses an identifier to mark the start and end of a multi line string.
• We need to know whether variables inside the heredoc content are parsed.
• We compare heredoc behaviour to single and double quoted strings.

Concept / Approach:
In PHP, single quoted strings treat most characters literally, and variables inside them are not expanded. Double quoted strings, by contrast, support variable interpolation and special escape sequences. Heredoc syntax behaves like a double quoted string. That means that if you place variables inside a heredoc, PHP will parse the content, convert variables to their values, and produce a final interpolated string. If you require no interpolation, you would use nowdoc syntax instead, which behaves like single quotes.

Step-by-Step Solution:
1. Recall that heredoc starts with three less than signs and an identifier, and ends with the same identifier on its own line. 2. Remember that documentation describes heredoc as similar to double quoted strings with respect to escape sequences and variable parsing. 3. Consider a simple example where a variable name appears inside a heredoc block. 4. Recognize that PHP will replace the variable placeholder with its value when the heredoc is evaluated. 5. Therefore, the correct statement about heredoc is that it supports variable substitution, like a double quoted string.

Verification / Alternative check:
You can verify this behaviour with a simple test script. Define a variable and then create a heredoc that includes that variable name in the text. When you echo the heredoc, you will see the variable value, not the literal variable name. This confirms that heredoc is parsed for variables. Repeating the same test with nowdoc syntax will show the opposite behaviour, which helps reinforce the difference.

Why Other Options Are Wrong:

• Option B is wrong because heredoc is not equivalent to single quoted strings; it does not treat variables purely as literal text.
• Option C is wrong because PHP does not selectively substitute only array elements; it processes variables in heredoc in the same general way as in double quoted strings.
• Option D is wrong because using variables inside heredoc does not cause a parse error; it is common practice in templates and email bodies.

Common Pitfalls:
A common mistake is confusing heredoc with nowdoc and assuming that heredoc will not parse variables. Another pitfall is misplacing the closing identifier or adding extra spaces, which will lead to parse errors unrelated to variable substitution. Developers should also be careful with complex variable expressions in heredoc and consider using braces for clarity. Understanding the interpolation rules helps you choose the appropriate string syntax for each situation.

Final Answer:
The correct statement is Yes, heredoc behaves like a double quoted string and supports variable substitution inside its contents, because PHP parses heredoc blocks in the same way it parses double quoted strings for variables and escape sequences.