Not all tables are as simple as they could be; most document authors aren’t experts in presenting tabular information. Navigating information presented in tables can be challenging enough for conventional users even with all the cues offered in the visual design. Many AT users are entirely reliant on an accurate encoding of the table’s structure, so ensuring the accuracy of table structures is a major responsibility for those verifying PDF files for accessibility.
At this point we assume that you’ve either encountered a tagged table or inserted a new table tag into the document. Some software generates PDF files in such a way that automatically generated tags fail to accurately represent the table structures present on a page. Accordingly, once it’s decided that a data table is present and thus table tags are appropriate, the next step is to verify that the table’s tags match the table structure as displayed on the page, and update the tags to match.
CommonLook PDF provides several mechanisms for verifying tables to suit a variety of workflows:
- In the Logical Structure Editor mode, table structure management is available on a per-page basis using the toolbar and menu items.
- In the Verify and Remediate mode, CommonLook PDF requires table verification when table tags are detected.
- In Section 508 and OK Standards modes, CommonLook PDF may be used to focus a work-session on tables alone using the Table Editor.
- The Table Editor provides support for page-spanning tables, linked headers, SpeakText and other advanced table structure managment features of CommonLook PDF.
No table is complete and correct until it’s a grid with the same number of cells in each row. In some cases it may be necessary to add and remove cells, rows or columns, or merge cells together to match the logic of the table presented on the PDF page.
Once text runs have been organized into cells that correctly reflect the table’s structure, empty cells need to be deleted, TH (table header) cells must be distinguished from TD (table data) cells and the scope must be set for the TH cells.
When one or more rows or cell tags are selected in the Logical Structure Editor, the table-management menu and toolbar options become available. When inserting a row or cell, CommonLook PDF gives the option to insert before or after the selected element via the drop down arrow to the right of the row and cell insertion tools.
When two or more cells are selected, the merge option (rowspan and colspan) becomes available. First select the cells to be merged in correct reading order (typically, left to right and/or top to bottom). In the resulting merged cell text runs will be arranged in the order of cell selection. It may be necessary to correct the order of the text runs after merging cells.
Moving text runs from one cell to another simply requires selecting and dragging them to the correct cell. As always when moving text runs within tags, make sure the text runs are placed in the correct reading order in each cell.
Once the table’s basic grid structure is correct the next step is to correctly tag and scope the header cells.
Headers (TH cells)
|<TH>↓ 1||<TH>↓ 2||<TH>↓ 3|
To make tabular information navigable by users with assistive technology, all assistive technology standards require the correct use of table header (<TH>) tags to represent cells that title a given column or row.
Typically, assistive technology will read out the header cells prior to reading the contents of subordinate header (<TH>) and data (<TD>) cells.
For example, a column header with “date”, would cause advanced screen reader to say “date” before reading the date in each cell below it. This helps users understand the context as the different rows and columns are read.
In addition to designation as a header cell, headers require a “scope”. The header’s scope defines the direction in the table to which the header applies, either column, row, or both.
Setting Scope for Table Header Cells
Select the table cells that should be designated as header cells and click the Properties tab below the physical window.
Change the type from TD to TH and set the scope property to Col (for column) or Row as appropriate.
In CommonLook PDF’s Section 508, OK Standards and Verify and Remediate modes, the Table Checkpoint stops and identifies tables with cells that don’t have headers specified. Clicking on a table checkpoint item in the Verification Results opens the Table Editor, in which various verification options are available.
In CommonLook PDF’s Logical Structure Editor you may initiate table verification on the selected table via the Verify and Remediate Table menu item under the Table menu.
While it’s possible to perform many table structure management functions in CommonLook PDF’s Logical Structure Editor, the dedicated Table Editor makes it easier to visualize how a given table’s tags will appear to assistive technology.
The Table Editor also provides advanced functionality for editing table structure, performing verification and supporting for software that doesn’t use tags in PDF. It’s especially useful for the following situations:
- Managing header cells and merged cells (colspans and rowspans).
- Complex tables that require restructuring, the use of linked headers, or that span tables.
- Verification without remediation, that is, identifying individual tables for remediation.
- Adding support for software that doesn’t understand tagged PDF.
As you begin using CommonLook PDF you will probably find table structure editing in the Logical Structure Editor seems more natural. Selections appear in context in the physical page view, and this makes things easier as you get used to the idea of how the physical page and the logical “view’ may differ.
As you continue to remediate PDF files this perspective may change. Once specific fixes to tables become obvious you may find it’s faster to use the Table Editor. Knowledge of both method of editing the logical structure of tables in CommonLook PDF will give you the widest range of options in terms of handling the situations you’ll encounter in PDF files, increasing efficiency so you can get more PDFs remediated with less effort in less time.