What character is commonly used to add a second level of column headers in tables?

The commonly used character for adding a second level of column headers in tables is the pipe symbol. The pipe character serves as a delimiter in various contexts, particularly in Markdown and certain table formatting systems. By using the pipe, you can create a clear separation between different columns and optionally provide a second header that can span multiple columns, enhancing readability and organization within the table.

For instance, when defining tables in Markdown, a pipe is used to separate the individual columns, making it a popular choice for structuring tabular data effectively. This character helps maintain a clean layout while distinctly showing the hierarchy and relationship between data fields, particularly beneficial when dealing with complex datasets or multi-level headers.

Other characters like the comma, semicolon, and slash do not fulfill the same role effectively in table formatting. Commas are typically used in CSV (Comma-Separated Values) files to separate values rather than as a structural element for headers. Semicolons and slashes also lack the same clarity and utility in delineating columns within the tabular format, rendering them less suitable than the pipe character for this purpose.