html - How to elegantly store email template strings in php

The html template of the email contains both single quotes and double quotes. Besides the original string, how can I write it in a more standardized way? It feels so messy to write the code using original strings. How can I make the code more elegant and beautiful

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The html template of the email contains both single quotes and double quotes. Besides the original string, how can I write it in a more standardized way? It feels so messy to write the code using original strings. How can I make the code more elegant and beautiful

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