There is no one correct answer. This wiki extract is helpful:
Programming identifiers often need to contain acronyms and initialisms
which are already in upper case, such as "old HTML file". By analogy
with the title case rules, the natural camel case rendering would have
the abbreviation all in upper case, namely "oldHTMLFile". However,
this approach is problematic when two acronyms occur together (e.g.,
"parse DBM XML" would become "parseDBMXML") or when the standard
mandates lower camel case but the name begins with an abbreviation
(e.g. "SQL server" would become "sQLServer"). For this reason, some
programmers prefer to treat abbreviations as if they were lower case
words and write "oldHtmlFile", "parseDbmXml" or "sqlServer".
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