Some are numeric and others contain letters.

有的是数字，有的则包含字母。

youdao

Note: the input string may contain letters other than the parentheses (and).

注意：输入字符串除了左右小括号外，还可能包含字母。

youdao

Web names can only contain letters, Numbers, periods, dashes, underscores and Spaces. Please enter a different name.

网站名称只能包含字母、数字、句点、连字符、下划线和空格。请输入其他名称。

youdao

The coded letters contain people's names, famous sayings and a website to help identify the cell.

VOA: special.2010.07.20

Some are thought to contain names and addresses, while others contain affectionate letters.

BBC: 'Entire streets' of Roman London uncovered in the City

Another advantage: These stretches can also be made to contain all the DNA letters that occur between genes.

FORBES: Magazine Article

Several more cases of using DNA sequencing, which reads out the 6 billion DNA letters that contain the protein recipes that make one person different from another, to understand the cause of disease have been published.

FORBES: Sequencing A Child's DNA -- And Convincing An Insurance Company To Pay