Highlight
Marking what someone searched for, inside the results. Nothing here goes near innerHTML — the text is split into pieces and rendered as text, so a search term can never become markup.
Type to mark
try “sep”, “paid”, or “<b>”
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INV-0241 Ferrow Manufacturing
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INV-0239 Northwind Trading
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INV-0236 Kestrel Logistics
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BILL-0117 Merrow Print
No note mentions “”.
As a plain mark
when the term is fixed rather than typed
The closing balance is $197,905.00, which agrees with the bank statement to 30 September. The difference against the ledger is nil — every one of the 214 transactions in the period is matched.
The <mark> element is the right tag for this: a screen reader can be told the text is marked, which a coloured <span> cannot convey.
Why not innerHTML
The quick way to highlight is to replace the term with <mark>$&</mark> and assign to innerHTML. That turns every search box on the page into a way to inject markup, and it only takes one field that echoes a name from a database for it to matter.
Splitting the string into hit and non-hit pieces and rendering each as text costs a few lines and closes that door completely. Type <b> into the box above — it is looked for, not executed.