Global Configuration

Inside of global settings there are some possibilities to be used. The "Default Case" is a field to select a standard of your classes. So if you select "Uppercase and Lowercase" but cases will be accepted. If you select "Uppercase" all classes will be added using uppercase and if you select "Lowercase" all classes added will be added using lowercase. Attention, if you change to only lowercase or only uppercase when save the block all block classes will be updated.

Field Type: By default the block class is using the field type as a "texfield", with that configuration you can select textarea as well, it's recommended if you have many classes per block

The max-length by default is 255, after the 2.0.x version there is a Global Settings Page and you can modify if you need at: /admin/config/content/block-class/settings or Configuration » Content authoring » Block Class

Allow only letters and numbers: If you select this checkbox the blocks will be filtered to allows only letters and numbers

Attributes
On this section you can use settings for attributes. 

Enable attributes: Mark this option to be able to use attributes. 

Field type: Inside of field group of attributes you can configure the field type. By default the attributes are you using textarea because with that you can insert more items using one per line. 

Maxlengh: In the attributes field group you can insert the maxlengh, by default there is no limit for attributes but you can insert if you want

Weight: Set the weight to organize better the field items in the block settings

ID:

• Enable id replacement, Mark this option to be able to use ID
• Maxlengh: In the ID field group you can insert the maxlengh, by default there is no limit for ID but you can insert if you want.
• Weight: Set the weight to organize better the field items in the block settings