What does it mean when text is underlined in blue

The blue underlined text is a grammar correction to give you suggestions. For example, if you make a sentence without enough, punctuation marks, then, the blue line will Appear, to suggest that you should put some punctuation in there - it is not a spell check.

However, I would like to add that it is completely useless and in fact very bothersome. Reason being, that, when you try to tap on the blue underlined word, to edit, the blue underlined word will select any text EXCEPT the blue underlined word. It is very difficult to click after the word, to put a comma or other punctuation mark, it will select the whole word, and make you delete it.

Sometimes, you know that it needs punctuation, but you don't want to put it, or you just want to change the last letter of the word. But the blue underlined text won't let you edit one single letter, it makes you have to redo the whole word, and so it's a very bothersome function which is useless to anybody.