Take the following example.
- Level 1-3: Wizard
- Level 4: Cleric
- Level 5: Wizard => I learn two new spells
Can I learn Fireball? (the arcane spell)
There is a line on (p. 58)
If you have more than one spellcasting class, this table might give you spell slots of a level that is higher than the spells you know or can prepare. You can use those slost, but only to cast your lower-level spells.
Based on the table, it looks like a Wizard 4 / Cleric 1 will have 2 spells slots at 3rd level. So this kind of sounds like "spell higher than I can prepare".
But, from the SRD (p. 51)
You prepare the list of wizards spells that are available for you to cast... The spells must be of a level for which you have spell slots.
Each time you gain a wizard level, you can add two wizard spells of your choice to your spellbook for free. Each of these spells must be of a level for which you have spells slots.
Based on this line, I do have 3rd level spell slots, so I can cast & learn Fireball. The text for Cleric is very similar and also seems to imply that Wizard 16 / Cleric 1 can cast True Ressurection.
However, I feel like 80% confident on this front. Has there been any errata / public clarification here? The SRD is only like a week old at this point.