What does the drop in
It'a punctuation, which does not exist in English, and I don't know its English name.
In Chinese it's called
Usually in English, comma would be used.
In your example, it is just used a symbol separating the listing number and the title, which is not related to the use I mentioned above. This is common when Chinese numbers are used. The punctuation itself does not carry actual meaning.
It's a comma, and it serves the same purpose as a colon in English. Somewhere further down in this lesson you'll see a 二 with a similar comma, followed by a heading, maybe 词汇.
It's a number with a Comma(顿号 in Chinese) and often appears in normal report or the text book for Chinese or something have relationship with social sciences.
I think "一.课文" is better. If you wirite it as “一 课文” is OK either.Maybe the editor stress the legitimacy of Chinese.
The comma dùn hào(顿号) is often used express pause between two word or among many word.The pause by comma is shorter than the comma dòu hào（逗号）
Like this 我喜欢足球、篮球、乒乓球、保龄球等。(I like playing football、basketball、pingpang、bowling and so on)
Here it's only a symbol to make the text look more normal. It appear sometimes in Chinese book.In other books like mathematic book or chemistry (science or engineering ) book we use 《.》 or not use a symbol more often.
While we're on this topic, you should also get used to:
《》 are equivalent title marks
那部电影的名字是《红高粱》: The title of that movie is Hong Gao Liang (Red Sorghum).
『...』 are quotation marks.
If you're reading verticle text, use this as quotation marks:
. . .