Wavy line for grammar error?

I'm sorry, I'm not sure what you mean by a "wavy line for grammar error." Can you please provide more context or clarify your question?

Yes, a wavy line under text is commonly used by word processors and text editors to indicate potential grammar errors. The wavy line typically appears beneath the word or phrase with the suspected error, and the color of the line may vary depending on the type of error detected. For example, red or orange lines may indicate critical errors such as misspellings or incorrect grammar, while green or blue lines may indicate minor issues such as stylistic suggestions or potential redundancies.